In-situ generation of heat treating atmospheres using a mixture of non-cryogenically produced nitrogen and a hydrocarbon gas

ABSTRACT

A process for generating in-situ low-cost atmospheres suitable for annealing and heat treating ferrous and non-ferrous metals and alloys, brazing metals, sealing glass to metals, and sintering metal and ceramic powders in a continuous furnace from non-cryogenically produced nitrogen containing up to 5% residual oxygen is presented. The disclosed process involves mixing nitrogen gas containing residual oxygen with a predetermined amount of a hydrocarbon gas, feeding the gaseous mixture through a nonconventional device into the hot zone of a continuous heat treating furnace, converting residual oxygen to an acceptable form such as a mixture of moisture and carbon dioxide, a mixture of moisture, hydrogen, carbon monoxide, and carbon dioxide, or a mixture of carbon monoxide, moisture, and hydrogen, and using the resultant gaseous mixture for annealing and heat treating metals and alloys, brazing metals, sintering metal and ceramic powders, and sealing glass to metals.

This is a division of application Ser. No. 07/787,982, now U.S. Pat. No.5,259,893 filed Nov. 5, 1991, which is a continuation-in-part of Ser.No. 07/727,806 filed Jul. 8, 1991, now U.S. Pat. No. 5,221,369.

FIELD OF THE INVENTION

The present invention pertains to preparing controlled furnaceatmospheres for heat treating metals, alloys, ceramics, compositematerials and the like.

BACKGROUND OF THE INVENTION

Nitrogen-based atmospheres have been routinely used by the heat treatingindustry both in batch and continuous furnaces since the mid seventies.Because of low dew point and virtual absence of carbon dioxide andoxygen, nitrogen-based atmospheres do not exhibit oxidizing anddecarburizing properties and are therefore suitable for a variety ofheat treating operations. More specifically, a mixture of nitrogen andhydrogen has been extensively used for annealing low to high carbon andalloy steels as well as annealing of non-ferrous metals and alloys suchas copper and gold. A mixture of nitrogen and a hydrocarbon such asmethane or propane has gained wide acceptance for neutral hardening anddecarburization-free annealing of medium to high carbon steels. Amixture of nitrogen and methanol has been developed and used forcarburizing of low to medium carbon steels. Finally, a mixture ofnitrogen, hydrogen, and moisture has been used for brazing metals,sintering metal and ceramic powders, and sealing glass to metals.

A major portion of nitrogen used by the heat treating industry has beenproduced by distillation of air in large cryogenic plants. Thecryogenically produced nitrogen is generally very pure and expensive. Toreduce the cost of nitrogen, several non-cryogenic air separationtechniques such as adsorption and permeation have been recentlydeveloped and introduced in the market. The non-cryogenically producednitrogen costs less to produce, however it contains from 0.05 to 5%residual oxygen, making a direct substitution of cryogenically producednitrogen with non-cryogenically produced nitrogen in continuousannealing and heat treating furnaces very difficult if not impossiblefor some applications. Several attempts have been made by researchers tosubstitute cryogenically produced nitrogen directly with that producednon-cryogenically but with limited success even with the use of anexcess amount of a reducing gas. The problem has generally been relatedto severe surface oxidation of the heat treated parts both in thecooling and heating zones of the furnace, resulting in rusting, scaling,and unacceptable metallurgical properties. The use of non-cryogenicallyproduced nitrogen has therefore been limited to applications wheresurface oxidation, rusting, and scaling can be tolerated. For example,non-cryogenically produced nitrogen has been successfully used in oxideannealing of carbon steel parts which are generally machined after heattreatment. Its use has, however, not been successful for brightannealing of finished carbon steel parts due to the formation of scaleand rust.

In the parent patent application referred to above a process forgenerating low-cost atmospheres inside continuous furnaces suitable forannealing and heat treating ferrous and non-ferrous metals alloys usingnon-cryogenically produced nitrogen and a reducing gas such as hydrogen,a hydrocarbon, or a mixture thereof was disclosed. The parentapplication described in detail processes for generating heat treatingatmospheres from non-cryogenically produced nitrogen and a reducing gas,particularly hydrogen.

SUMMARY OF THE INVENTION

The present invention pertains to processes for generating in-situ lowcost atmospheres suitable for annealing and heat treating ferrous andnon-ferrous metals and alloys, brazing metals, sintering metal andceramic powders, and sealing glass to metals in continuous furnaces fromnon-cryogenically produced nitrogen. According to the processes,suitable atmospheres are generated by 1) mixing non-cryogenicallyproduced nitrogen containing up to 5% residual oxygen with a hydrocarbongas, 2) feeding the gas mixture into continuous furnaces having a hotzone operated at temperatures above between about 700° C. and about1,250° C. in a defined way or step, and 3) converting the residualoxygen to an acceptable form such as a mixture of moisture and carbondioxide, a mixture of moisture, hydrogen, carbon monoxide, and carbondioxide, or a mixture of carbon monoxide, moisture, and hydrogen. Theprocesses utilize the gas feeding device disclosed in the aforementionedapplication which device helps in converting residual oxygen present inthe feed to an acceptable form prior to coming in contact with the partsto be heat treated. The gas feeding device can be embodied in many formsso long as it can be positioned for introduction of the atmospherecomponents into the furnace in a manner to promote conversion of theoxygen in the feed gas to an acceptable form prior to coming in contactwith the parts. In some cases, the gas feeding device can be designed ina way that it not only helps in the conversion of oxygen in the feed gasto an acceptable form but also prevents the direct impingement of feedgas with unreacted oxygen on the parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a controlled atmosphere heattreating furnace illustrating atmosphere introduction into thetransition or cooling zone of the furnace.

FIG. 2 is a schematic representation of a controlled atmosphere heattreating furnace illustrating atmosphere introduction into the hot zoneof the furnace.

FIG. 3A is a schematic representation of an open tube device accordingto present invention for introducing atmosphere into a heat treatingfurnace.

FIG. 3B is a schematic representation of an open tube and baffle deviceaccording to present invention for introducing atmosphere into a heattreating furnace.

FIG. 3C is a schematic representation of a semi-porous device accordingto present invention for introducing atmosphere into a heat treatingfurnace.

FIG. 3D is a schematic representation of an alternate configuration of asemi-porous device according to present invention used to introduceatmosphere into a furnace.

FIG. 3E and 3F are schematic representations of other porous devicesaccording to present invention for introducing atmosphere into a heattreating furnace.

FIG. 3G is a schematic representation of a concentric porous deviceinside a porous device according to present invention for introducingatmosphere into a heat treating furnace.

FIG. 3H and 3I are schematic representations of concentric porousdevices according to present invention for introducing atmosphere into aheat treating furnace.

FIG. 4 is a schematic representation of a furnace used to test the heattreating processes according to the present invention.

FIG. 5 is a plot of temperature against length of the furnaceillustrating the experimental furnace profile for a heat treatingtemperature of 750° C.

FIG. 6 is a plot similar to that of FIG. 5 for a heat treatingtemperature of 950° C.

FIG. 7 is a plot of annealing temperature against natural gasrequirement for annealing carbon steel according to the invention.

FIG. 8 is a plot of annealing temperature against natural gasrequirement for annealing carbon steel according to the invention.

FIG. 9 is a plot of annealing temperature against propane requirementfor annealing carbon steel according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to processes for generating low-costatmospheres suitable for annealing and heat treating ferrous andnon-ferrous metals and alloys in continuous furnaces usingnon-cryogenically produced nitrogen. The processes of the presentinvention are based on the surprising discovery that atmospheressuitable for annealing and heat treating ferrous and non-ferrous metalsand alloys, brazing metals, sintering metal and ceramic powders, andsealing glass to metals can be generated inside a continuous furnacefrom non-cryogenically produced nitrogen by mixing it with a hydrocarbongas in a predetermined proportion and feeding the mixture into the hotzone of the furnace through a non-conventional device that facilitatesconversion of residual oxygen present in non-cryogenically producednitrogen to an acceptable form prior to coming in contact with the partsand/or prevents the direct impingement of feed gas on the parts.

Nitrogen gas produced by cryogenic distillation of air has been widelyemployed in many annealing and heat treating applications. Cryogenicallyproduced nitrogen is substantially free of oxygen (oxygen content hasgenerally been less than 10 ppm) and very expensive. Therefore, therehas been a great demand, especially by the heat treating industry, togenerate nitrogen inexpensively for heat treating applications. With theadvent of non-cryogenic technologies for air separation such asadsorption and permeation, it is now possible to produce nitrogen gasinexpensively. The non-cryogenically produced nitrogen, however, iscontaminated with up to 5% residual oxygen, which is generallyundesirable for many heat treating applications. The presence ofresidual oxygen has made the direct substitution of cryogenicallyproduced nitrogen for that produced by non-cryogenic techniques verydifficult.

Several attempts to substitute cryogenically produced nitrogen for thatproduced non-cryogenically in continuous furnaces have met limitedsuccess even when using additions of excess amounts of hydrocarbon gas.The metallic parts treated with non-cryogenically produced nitrogen werealways scaled, rusted, or oxidized. These problems are believed to becaused by the introduction of the gaseous feed mixture through an opentube in the transition (or shock) zone located between the heating andthe cooling zones of continuous furnaces. The introduction ofnon-cryogenically produced nitrogen premixed with a hydrocarbon gas inthe transition or cooling zone does not allow residual oxygen present inthe feed gas to react with the reducing gas, resulting in oxidation ofthe parts in the cooling zone. This is a conventional way of introducingfeed gas into continuous furnaces and is shown in FIG. 1 where 10denotes the furnace having an entry end 12 and a discharge end 14. Parts16 to be treated are moved through furnace 10 by means of an endlessconveyor 18. Furnace 10 can be equipped with entry and exit curtains 20,22 respectively to help maintain the furnace atmosphere, a techniqueknown in the art. As shown in FIG. 1 an atmosphere is injected into thetransition zone, located between the hot zone and the cooling zone bymeans of pipe or tube like device 24.

To improve the rate and extent of reaction between residual oxygen and ahydrocarbon gas, attempts have been made to introduce gaseous feedmixture directly into the hot zone of a continuous furnace 10 using aconventional open feed tube 24, as shown in FIG. 2. Parts treated bythis method were found to be scaled, rusted or oxidized non-uniformly.

According to the present invention scaling, rusting, and non-uniformoxidation can be prevented by the process of feeding gaseous mixturesinto the furnace in a specific manner so that the residual oxygenpresent in the feed gas is reacted with a hydrocarbon gas and convertedto an acceptable form prior to coming in contact with the parts. Thiswas accomplished by introducing the gaseous feed mixture into the hotzone of the furnace using devices which prevent the direct impingementof feed gas on the parts and/or to help in converting residual oxygenpresent in the gaseous feed mixture by reaction with a hydrocarbon gasto an acceptable form prior to coming in contact with the parts. Devicesused to effect the processes of the present invention are shown in FIGS.3A through 3I and discussed in detail in the specification of ourcopending application referred to above.

A continuous furnace operated at atmospheric or above atmosphericpressure with separate heating and cooling zones is most suitable forthe processes of the present invention. The continuous furnace can be ofthe mesh belt, a roller hearth, a pusher tray, a walking beam, or arotary hearth type.

A continuous furnace operated at atmospheric or above atmosphericpressure with a heating zone and an integrated quench cooling zone isalso suitable for the processes of the present invention. The continuousfurnaces can be a mesh belt, shaker, a roller hearth, a pusher tray, ora rotary hearth type.

The residual oxygen in non-cryogenically produced nitrogen can vary from0.05% to about 5%. It can preferably vary from about 0.05% to about 3%.More preferably, it can vary from about 0.05% to about 1.0%.

The hydrocarbon gas can be selected from the group consisting of ahydrocarbon, an alcohol, an ether, or mixtures thereof. The hydrocarbongas can be selected from alkanes such as methane, ethane, propane, andbutane; alkenes such as ethylene, propylene, and butene; alcohols suchas methanol, ethanol, and propanol; and ethers such as dimethyl ether,diethyl ether, and methyl-ethyl ether. Commercial feedstocks such asnatural gas, petroleum gas, cooking gas, coke oven gas, town gas,exothermic gas, and endothermic gas can also be used as a reducing gas.

A hydrocarbon selected from alkanes, alkenes, ethers, alcohols,commercial feedstocks, and their mixtures can be used in the furnaceoperating at temperatures from about 700° C. to about 1,250° C.,preferably used in the furnaces operating between 800° C. to about1,250° C. The selection of the amount of a hydrocarbon gas depends uponthe treatment temperature and the composition and reactivity of thehydrocarbon gas. For example, the amount of natural gas required forcontrolled oxide annealing of low to high carbon steel is between 1.0and below about 5.0 times the stoichiometric amount at 1,100° C.;whereas, it is between 1.0 and below about 1.5 times the stoichiometricamount for propane at the same temperature. This is due to the fact thatpropane is more reactive with oxygen than natural gas (the auto-ignitiontemperature of propane is 450° C. versus 630° C. for natural gas). Theterm stoichiometric amount stands for the amount of hydrocarbon gasrequired for converting residual oxygen present in the non-cryogenicallyproduced nitrogen to a mixture of moisture and carbon dioxide. Theamount of a hydrocarbon gas required for oxide annealing increases witha decrease in the temperature. For example, the amount of natural gasrequired at 1,050° C. is between 1.0 and below about 6.0 times thestoichiometric amount. The amount of propane required for oxideannealing at 1,050° C. is between 1.0 and below about 1.7 times thestoichiometric amount. Likewise, the amount of natural gas required at1,000° C., 950° C., and 850° C. is greater than 1.0 times but belowabout 10.0, 24.0, and 40.0 times the stoichiometric amount,respectively. Similarly, the about of propane at 1,000° C. and 950° C.is greater than 1.0 times but below about 1.9 and 3.2 times thestoichiometric amount, respectively.

The bright, oxide-free and partially decarburized annealing of low tohigh carbon steel is carried out at temperatures between about 800° C.and 1,250° C. The amount of a hydrocarbon gas required for producingatmospheres suitable for bright, oxide-free, and partially decarburizedannealing of low to high carbon steel depends upon the furnacetemperature and the reactivity of the hydrocarbon used. For example, theamount of natural gas required is above about 5.0 times thestoichiometric amount at 1,100° C.; whereas, it is above about 1.5 timesthe stoichiometric amount for propane at the same temperature. Theamount of a hydrocarbon gas required for bright annealing increases witha decrease in the temperature. For example, the amount of natural gasrequired at 1,050° C. is above about 6.0 times the stoichiometricamount. The amount of propane required at 1,050° C. is above about 1.7times the stoichiometric amount. Likewise, the amount of natural gasrequired at 1,000° C., 950° C., and 850° C. is above about 10.0, 24.0,and 40.0 times the stoichiometric amount, respectively. Similarly, theamount of propane at 1,000° C. and 950° C. is above about 1.9 and 3.2times the stoichiometric amount, respectively.

The bright, oxide-free and partially decarburized, oxide-free anddecarburized-free, or oxide-free and partially carburized annealing oflow to high carbon steel annealing of low to high carbon steel is alsocarried out at temperatures between about 800° C. and 1,250° C. Theamount of a hydrocarbon gas required for producing atmosphere suitablefor bright, oxide-free and partially decarburized, oxide-free anddecarburized-free, or oxide-free and partially carburized annealing oflow to high carbon steel also depends upon the furnace temperature andthe reactivity of the hydrocarbon used. For example, the amount ofnatural gas required is above about 5.0 times the stoichiometric amountat 1,100° C.; whereas, it is above about 1.5 times the stoichiometricamount for propane at the same temperature. The amount of a hydrocarbongas required also increases with a decrease in the temperature. Forexample, the amount of natural gas required at 1,050° C. is above about6.0 times the stoichiometric amount. The amount of propane required at1,050° C. is above about 1.7 times the stoichiometric amount. Likewise,the amount of natural gas required at 1,000° C., 950° C., and 850° C. isabove about 10.0, 24.0, and 40.0 times the stoichiometric amount,respectively. Similarly, the amount of propane at 1,000° C. and 950° C.is above about 1.9 and 3.2 times the stoichiometric amount,respectively.

The brazing of metals, sealing of glass to metals, sintering of metaland ceramic powders, or annealing of non-ferrous alloys is carried outat temperatures between about 800° C. and 1,250° C. The amount of ahydrocarbon gas required for these operations depends upon the furnacetemperature and the reactivity of the hydrocarbon used. For example, theamount of natural gas required is above about 5.0 times thestoichiometric amount at 1,100° C.; whereas, it is above about 1.5 timesthe stoichiometric amount for propane at the same temperature. Theamount of a hydrocarbon gas required for these operations increases witha decrease in the temperature. For example, the amount of natural gasrequired at 1,050° C. is above 6.0 times the stoichiometric amount. Theamount of propane required at 1,050° C. is above about 1.7 times thestoichiometric amount. Likewise, the amount of natural gas required at1,000° C., 950° C., and 850° C. is above about 10.0, 24.0, and 40.0times the stoichiometric amount, respectively. Similarly, the amount ofpropane at 1,000° C. and 950° C. is above about 1.9 and 3.2 times thestoichiometric amount, respectively.

The non-cryogenically produced nitrogen or the mixture ofnon-cryogenically produced nitrogen and hydrocarbon gaseous feed canoptionally be preheated close to the heat treatment temperature prior tointroducing it into the furnace. Preheating the nitrogen or the nitrogenand hydrocarbon gas mixture would tend to lower the minimum temperaturerequired and the amount of hydrocarbon required for annealing ferrousand non-ferrous metals and alloys, brazing metals, sintering metal andceramic powders, and sealing glass to metals according to the processesof the invention. The gaseous feed can be preheated using an externalheater or within the furnace by passing it through a heating tube placedinside the furnace.

A small amount of hydrogen can optionally be added to the mixture ofnon-cryogenically produced nitrogen and hydrocarbon gas prior tointroducing the gaseous feed into the hot zone of the furnace to furtherexpand the operating window for annealing ferrous and non-ferrous metalsand alloys, brazing metals, sintering metal and ceramic powders, andsealing glass to metals. The amount of hydrogen added can vary fromabout 0.1 times to about 5.0 times the stoichiometric amount requiredfor converting residual oxygen present in the non-cryogenically producednitrogen to moisture. The hydrogen gas can be supplied from gas orliquid hydrogen tanks. Optionally, it can be produced and suppliedon-site by dissociating ammonia to a mixture of hydrogen and nitrogen.

Low and high carbon or alloy steels that can be heat treated accordingto the present invention can be selected from the groups 10XX, 11XX,12XX, 13XX, 15XX, 40XX, 41XX, 43XX, 44XX, 46XX, 47XX, 48XX, 50XX, 51XX,61XX, 81XX, 86XX, 87XX, 88XX, 92XX, 93XX, 50XXX, 51XXX, or 52XXX asdescribed in Metals Handbook, Ninth Edition, Volume 4 Heat Treating,published by American Society for Metals. Tool steels selected from thegroups AX, DX, OX, MX, or SX, iron nickel based alloys such as Incoloy,nickel alloys such as Inconel and Hastalloy, nickel-copper alloys suchas Monel, cobalt based alloys such as Haynes and stellite can be heattreated according to processes disclosed in this invention.

In order to demonstrate the invention a series of annealing and heattreating tests were carried out in a Watkins-Johnson conveyor beltfurnace capable of operating up to a temperature of 1,150° C. Theheating zone of the furnace consisted of 8.75 inches wide, about 4.9inches high, and 86 inches long Inconel 601 muffle heated resistivelyfrom the outside. The cooling zone, made of stainless steel, was 8.75inches wide, 3.5 inches high, and 90 inches long and was water cooledfrom the outside. An 8.25 inches wide flexible conveyor belt supportedon the floor of the furnace was used to feed the samples to be heattreated through the heating and cooling zones of the furnace. A fixedbelt speed of about 6 inches per minute was used in all the experiments.The furnace shown schematically as 60 in FIG. 4 was equipped withphysical curtains 62 and 64 both on entry 66 and exit 68 sections toprevent air from entering the furnace. The gaseous feed mixturecontaining non-cryogenically produced nitrogen premixed with ahydrocarbon base, was introduced into the transition zone via an opentube introduction device 70 or through one of the introduction devices72, 74, 76 placed at different locations in the heating or hot zone ofthe furnace 60. Introduction devices 72, 74, 76 can be any one of thetypes shown in FIGS. 3A through 3I of the drawing. These hot zone feedlocations 72, 74, 76 were located 12 inches, 30 inches, and 40 inches,respectively from the transition zone and they were located well intothe hottest section of the hot zone as shown by the furnace temperatureprofiles depicted in FIGS. 5 and 6 obtained for 750° C. and 950° C.normal furnace operating temperatures with 350 SCFH of pure nitrogenflowing into furnace 60. The temperature profiles show a rapid coolingof the parts as they move out of the heating zone and enter the coolingzone. Rapid cooling of the parts is commonly used in annealing and heattreating to help in preventing oxidation of the parts from high levelsof moisture and carbon dioxide often present in the cooling zone of thefurnace. The tendency for oxidation is more likely in the furnacecooling zone since a higher pH₂ /pH₂ O, and pCO/pCO₂ are needed at lowertemperatures where H₂ and CO are less reducing and CO₂ and H₂ O are moreoxidizing.

A heat treating temperature between 750° C. to 1,100° C. was selectedand used for heat treating 0.2 inch thick flat low-carbon steelspecimens approximately 8 inches long by 2 inches wide. As shown in FIG.4, the atmosphere composition present in the heating zone of the furnace60 was determined by taking samples at locations designated S1 and S2and samples were taken at locations S3 and S4 to determine atmospherecomposition in the cooling zone. The samples were analyzed for residualoxygen, moisture (dew point), hydrogen, hydrocarbon, CO, and CO₂.

Several experiments were carried out to study annealing of carbon steelusing non-cryogenically produced nitrogen premixed with natural gascontaining predominantly methane at temperatures varying 750° C. to1,100° C. The feed gas was introduced in the transition zone or theheating zone through a straight open-ended tube simulating theconventional method of introducing gas into the furnace. The results ofthese experiments are set out in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                       Example 1-1                                                                          Example 1-2                                                                          Example 1-3                                                                          Example 1-4                                                                          Example 1-5                                                                          Example                 __________________________________________________________________________                                                          1-6A                    Heat Treatment Temperature, °C.                                                           1,100  1,100  1,100  1,100  1,100  950                     Flow Rate of Feed Gas, SCFH                                                                      350    350    350    350    350    350                     Feed Gas Location  Transition                                                                           Transition                                                                           Transition                                                                           Transition                                                                           Transition                                                                           Transition                                 Zone   Zone   Zone   Zone   Zone   Zone                    Type of Feed Device                                                                              Open Tube                                                                            Open Tube                                                                            Open Tube                                                                            Open Tube                                                                            Open Tube                                                                            Open Tube               Feed Gas Composition                                                          Nitrogen, %        99.50  99.50  99.50  99.50  99.50  99.50                   Oxygen, %          0.50   0.50   0.50   0.50   0.50   0.50                    Natural Gas* (Methane), %                                                                        0.25   0.50   1.00   2.00   3.00   0.25                    Heating Zone Atmosphere Composition                                           Oxygen, ppm        <2     <2     <5     <2     <4     <7                      Carbon Monoxide, % --     0.50   1.00   0.95   1.00   0.00                    Carbon Dioxide, %  --     0.01   0.00   0.00   0.00   0.19                    Hydrogen, %        --     1.30   1.50   3.00   >5.00  0.25                    Methane, %         0.03   0.11   0.23   0.42   0.53   0.03                    Dew Point, °C.                                                                            --     -31.0  -31.5  -33.9  -44.0  -2.9                    Cooling Zone Atmosphere Composition                                           Oxygen, ppm        5,000  5,000  5,000  4,500  4,100  4,900                   Carbon Monoxide, % 0.00   0.00   0.00   0.00   0.00   0.00                    Carbon Dioxide, %  0.00   0.00   0.01   0.02   0.04   0.00                    Hydrogen, %        0.00   0.00   0.05   0.15   0.20   0.00                    Methane, %         0.25   0.50   0.98   1.92   2.96   0.24                    Dew Point, °C.                                                                            -34.0  -31.4  -27.8  -21.4  -20.1  -29.0                   Quality of Heat Treated Samples                                                                  Non-Uniform                                                                          Non-Uniform                                                                          Non-Uniform                                                                          Non-Uniform                                                                          Non-Uniform                                                                          Uniform,                                   Oxide  Oxide  Oxide  Oxide  Oxide  Tightly                                                                       Packed                  __________________________________________________________________________                                                          Oxide                                      Example 1-6B                                                                         Example 1-6C                                                                          Example 1-7                                                                          Example 1-8                                                                          Example                                                                               Example               __________________________________________________________________________                                                            1-9B                  Heat Treatment Temperature, °C.                                                           950    950     950    950    850     850                   Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350     350                   Feed Gas Location  Transition                                                                           Transition                                                                            Transition                                                                           Transition                                                                           Transition                                                                            Transition                               Zone   Zone    Zone   Zone   Zone    Zone                  Type of Feed Device                                                                              Open Tube                                                                            Open Tube                                                                             Open Tube                                                                            Open Tube                                                                            Open Tube                                                                             Open Tube             Feed Gas Composition                                                          Nitrogen, %        99.50  99.50   99.50  99.50  99.50   99.50                 Oxygen, %          0.50   0.50    0.50   0.50   0.50    0.50                  Natural Gas* (Methane), %                                                                        0.50   1.00    2.00   3.00   0.35    0.50                  Heating Zone Atmosphere Composition                                           Oxygen, ppm        <6     <6      <3     <4     18      14                    Carbon Monoxide, % 0.05   0.25    0.90   --     0.25    0.25                  Carbon Dioxide, %  0.12   0.09    0.00   0.00   0.11    0.10                  Hydrogen, %        0.20   0.50    2.90   >5.00  0.30    0.35                  Methane, %         0.25   0.64    1.10   1.40   0.07    0.20                  Dew Point, °C.                                                                            1.2    --      -29.3  -34.0  -9.3    -10.0                 Cooling Zone Atmosphere Composition                                           Oxygen, ppm        4,900  4,800   4,300  4,000  4,800   4,800                 Carbon Monoxide, % 0.00   0.00    0.00   0.00   0.00    0.00                  Carbon Dioxide, %  0.00   0.00    0.01   0.01   0.01    0.02                  Hydrogen, %        0.05   0.10    0.15   0.20   0.10    0.10                  Methane, %         0.48   0.98    1.96   2.96   0.36    0.50                  Dew Point, °C.                                                                            --     -27.0   -18.0  -19.0  -33.1   -29.3                 Quality of Heat Treated Samples                                                                  Uniform,                                                                             Uniform,                                                                              Non-Uniform                                                                          Non-Uniform                                                                          Uniform,                                                                              Uniform,                                 Tightly                                                                              Tightly Oxide  Oxide  Tightly Tightly                                  Packed Oxide                                                                         Packed Oxide          Packed Oxide                                                                          Packed                __________________________________________________________________________                                                            Oxide                                    Example 1-9C                                                                           Example 1-9D                                                                          Example 1-10A                                                                          Example 1-10B                                                                          Example                 __________________________________________________________________________                                                          1-10C                   Heat Treatment Temperature, °C.                                                           850      850     750      750      750                     Flow Rate of Feed Gas, SCFH                                                                      350      350     350      350      350                     Feed Gas Location  Transition                                                                             Transition                                                                            Transition                                                                             Transition                                                                             Transition                                 Zone     Zone    Zone     Zone     Zone                    Type of Feed Device                                                                              Open Tube                                                                              Open Tube                                                                             Open Tube                                                                              Open Tube                                                                              Open Tube               Feed Gas Composition                                                          Nitrogen, %        99.50    99.50   99.50    99.50    99.50                   Oxygen, %          0.50     0.50    0.50     0.50     0.50                    Natural Gas* (Methane), %                                                                        1.00     2.00    0.25     0.50     1.00                    Heating Zone Atmosphere Composition                                           Oxygen, ppm        <10      <6      1,300    600      55                      Carbon Monoxide, % 0.50     0.85    0.00     0.00     0.10                    Carbon Dioxide, %  0.06     0.03    0.11     0.15     0.15                    Hydrogen, %        1.00     2.30    0.10     0.20     0.40                    Methane, %         0.51     1.10    0.16     0.37     0.77                    Dew Point, °C.                                                                            -12.0    -18.4   -13.3    -7.6     -4.1                    Cooling Zone Atmosphere Composition                                           Oxygen, ppm        4,500    4,300   4,800    4,600    4,400                   Carbon Monoxide, % 0.00     0.00    0.00     0.00     0.00                    Carbon Dioxide, %  0.02     0.03    0.01     0.01     0.02                    Hydrogen, %        0.40     0.50    0.10     0.15     0.30                    Methane, %         1.00     1.96    0.24     0.48     0.97                    Dew Point, °C.                                                                            -24.6    -22.3   -40.1    -34.3    -32.1                   Quality of Heat Treated Samples                                                                  Uniform, Uniform,                                                                              Uniform, Uniform  Uniform,                                   Tightly  Tightly Tightly  Tightly  Tightly                                    Packed Oxide                                                                           Packed Oxide                                                                          Packed Oxide                                                                           Packed Oxide                                                                           Packed                  __________________________________________________________________________                                                          Oxide                                      Example 1-10D                                                                         Example 1-11                                                                         Example 1-12                                                                         Example 1-13                                                                         Example                                                                              Example                __________________________________________________________________________                                                           1-18                   Heat Treatment Temperature, °C.                                                           750     1,100  1,100  1,100  1,100  950                    Flow Rate of Feed Gas, SCFH                                                                      350     350    350    350    350    350                    Feed Gas Location  Transition                                                                            Heating Zone                                                                         Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              Zone    (Location 74)                                                                        (Location 74)                                                                        (Location 74)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Open Tube                                                                             Open Tube                                                                            Open Tube                                                                            Open Tube                                                                            Open Tube                                                                            Open Tube              Feed Gas Composition                                                          Nitrogen, %        99.50   99.50  99.50  99.50  99.50  99.50                  Oxygen, %          0.50    0.50   0.50   0.50   0.50   0.50                   Natural Gas* (Methane), %                                                                        2.00    0.25   0.50   1.00   3.00   0.25                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        18      <7     <5     <7     <5     <3                     Carbon Monoxide, % 0.35    --     0.50   0.90   1.00   0.15                   Carbon Dioxide, %  0.10    0.20   0.06   0.00   0.00   0.12                   Hydrogen, %        0.15    --     0.70   1.70   >5.0   0.30                   Methane, %         1.58    0.03   0.08   0.17   0.34   0.01                   Dew Point, °C.                                                                            -9.1    +2.0   -9.4   -25.4  -26.0  -8.3                   Cooling Zone Atmosphere Composition                                           Oxygen, ppm        4,100   700    64     55     30     <4                     Carbon Monoxide, % 0.00    0.00   0.15   0.40   1.00   0.10                   Carbon Dioxide, %  0.04    0.20   0.12   0.06   0.01   0.18                   Hydrogen, %        0.65    0.00   0.30   1.00   ˜5.00                                                                          0.25                   Methane, %         1.95    0.03   0.09   0.48   1.90   0.02                   Dew Point, °C.                                                                            -27.5   7.1    9.4    5.2    -23.8  -3.1                   Quality of Heat Treated Samples                                                                  Uniform,                                                                              Non-Uniform                                                                          Non-Uniform                                                                          Non-Uniform                                                                          Mixture                                                                              Non-Uniform                               Tightly Oxide  Oxide  Oxide  Bright and                                                                           Oxide                                     Packed Oxide                 Oxide                         __________________________________________________________________________     *Natural gas was mixed with nitrogen and added as a percent of total          noncryogenically produced nitrogen.                                      

The following summary of the data presented in Table 1 illustrates oneaspect of the invention.

EXAMPLE 1-1

Samples of carbon steels described earlier were annealed at 1,100° C. inthe Watkins-Johnson furnace using 350 SCFH of nitrogen containing 99.5%N₂ and 0.5% O₂. The gaseous feed nitrogen was similar in composition tothat commonly produced by non-cryogenic air separation techniques. Itwas mixed with 0.25% natural gas consisting of predominately methane.This amount of natural gas was equal to the stoichiometric amountrequired for the complete conversion of residual oxygen present in thefeed nitrogen completely to a mixture of carbon dioxide and moisture.The gaseous feed mixture was introduced into the furnace through a 3/4in. diameter tube located in the transition zone (location 70 in FIG. 4)of the furnace as is conventionally practiced in the heat treatingindustry. A part of the gaseous feed mixture traveled from thetransition zone into the heating zone and exited through the entrycurtain 62. This part of the feed mixture had an opportunity to heat upand cause natural gas and residual oxygen to react. The remaining feedgas traveled through the cooling zone and exited through the exitcurtain 64. This part of the feed gas had no opportunity to heat up andcause residual oxygen to react with the natural gas. The gaseous feedmixture was passed through the furnace for at least one hour to purgeand condition the furnace prior to heat treating the samples.

The steel samples heat treated in this example were found to be oxidizednon-uniformly. The residual oxygen present in the portion of the feedgas travelling through the heating zone was reacted with natural gas andconverted to a mixture of carbon dioxide and moisture. The surface ofthe samples were oxidized non-uniformly in the cooling zone due to thepresence of a large amount of residual oxygen (see Table 1). It isbelieved the non-uniform oxidation was due to uncontrolled oxidation athigh temperature in the heating zone and/or high cooling rate in thecooling zone.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith a stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an unacceptable process for oxide annealing or brightannealing steel at 1,100° C.

EXAMPLE 1-2

The carbon steel annealing experiment described in Example 1-1 wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 0.50% natural gasto the feed gas with the amount of natural gas being 2.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe oxidized non-uniformly. The presence of high pCO/pCO₂ (>2.8) and pH₂/pH₂ O (>1.3) ratios in the heating zone probably caused the surface ofthe samples to reduce in the heating zone (see Table 1), but the samplesoxidized non-uniformly in the cooling zone due to presence of largeamount of residual oxygen. Thus the introduction of non-cryogenicallyproduced nitrogen pre-mixed with two times the stoichiometric amount ofnatural gas into a continuous heat treating furnace through an open tubelocated in the transition zone would result in an unacceptable processfor oxide annealing or bright annealing steel at 1,100° C.

EXAMPLES 1-3 TO 1-5

The carbon steel annealing experiment described in Example 1-2 wasrepeated three times using the same furnace, temperature, samples,location of feed gas, nature of feed gas device, flow rate andcomposition of feed gas, and annealing procedure with the exception ofadding 1.0, 2.0, and 3.0% natural gas to the feed gas with the amount ofnatural gas being 4.0, 8.0, and 12.0 times stoichiometric amount,respectively, required for converting residual oxygen present in thefeed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with these procedures were found tobe oxidized non-uniformly. Thus the introduction of non-cryogenicallyproduced nitrogen pre-mixed with 4.0, 8.0, and 12.0 times thestoichiometric amount of natural gas into a continuous heat treatingfurnace through an open tube located in the transition zone would resultin an unacceptable process for oxide annealing or bright annealing steelat 1,100° C.

EXAMPLE 1-6A

The carbon steel annealing experiment described in Example 1-1 wasrepeated using the same furnace, samples, location of feed gas, natureof feed gas device, flow rate and composition of feed gas, and annealingprocedure with the exception of using 950° C. temperature. The amount ofnatural gas added in this example was equal to the stoichiometric amountrequired for converting residual oxygen present in the feed nitrogen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating zone toa mixture of carbon dioxide and moisture. The presence of low pCO/pCO₂(<2.4) and pH₂ /pH₂ O (<1.6) ratios probably oxidized the surface of thesamples in the heating zone. The surface of the samples was oxidizedfurther in the cooling zone due to the presence of large amount ofresidual oxygen (see Table 1), resulting in uniform and controlledoxidation of the surface of the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 950°C. However, it would not result in an acceptable process for brightannealing steel at 950° C.

EXAMPLE 1-6B

The carbon steel annealing experiment described in Example 1-6A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 0.50% natural gasto the feed gas with the amount of natural gas being 2.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with twotimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 950°C.

EXAMPLE 1-6C

The carbon steel annealing experiment described in Example 1-6A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 1.0% natural gas tothe feed gas with the amount of natural gas being 4.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating zone toa mixture of carbon monoxide, carbon dioxide, and moisture, as shown inTable 1. The surface of the samples was oxidized uniformly in thecooling zone due to the presence of large amount of residual oxygen (seeTable 1), resulting in uniform and controlled oxidation of the surfaceof the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith four times the stoichiometric amount of natural gas into acontinuous heat treating furnace through an open tube located in thetransition zone would result in an acceptable process for oxideannealing steel at 950° C. However, it would not result in an acceptableprocess for bright annealing steel at 950° C. The result of this exampleshowed that it is desirable to maintain either pCO/pCO₂ ratio lower than2.4 or pH₂ /pH₂ O ratio lower than 1.6 in the heating zone to produceuniform and controlled oxide surface on the steel samples.

EXAMPLES 1-7 AND 1-8

The carbon steel annealing experiment described in Example 1-6A wasrepeated two times using the same furnace, temperature, samples,location of feed gas, nature of feed gas device, flow rate andcomposition of feed gas, and annealing procedure with the exception ofadding 2.0 and 3.0% natural gas to the feed gas with the amount ofnatural gas being 8.0 and 12.0 times stoichiometric amount,respectively, required for converting residual oxygen present in thefeed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with these procedures were found tobe oxidized non-uniformly. The residual oxygen present in the feednitrogen was converted in the heating zone to a mixture of carbonmonoxide and moisture. The presence of high pCO/pCO₂ (>2.4) and pH₂ /pH₂O (>1.6) ratios in the heating zone probably reduced the surface of thesamples, but the surface of the samples oxidized non-uniformly in thecooling zone due to the presence of large amount of residual oxygen inthe cooling zone (see Table 1).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 8.0, and 12.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through an open tube located in thetransition zone would result in an unacceptable process for oxideannealing or bright annealing steel at 950° C. The result of theseexamples showed that it is desirable to maintain low pCO/pCO₂ ratio(<2.4) or pH₂ /pH₂ O ratio (<1.6) in the heating zone to produce uniformand controlled oxide surface on the steel samples.

EXAMPLE 1-9A

The carbon steel annealing experiment described in Example 1-1 wasrepeated using the same furnace, samples, location of feed gas, natureof feed gas device, flow rate and composition of feed gas, and annealingprocedure with the exceptions of using 0.35% natural gas and 850° C.temperature. The amount of natural gas added in this example was equalto 1.4 times the stoichiometric amount required for converting residualoxygen present in the feed nitrogen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with morethan stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 850°C. However, it would not result in an acceptable process for brightannealing steel at 850° C.

EXAMPLE 1-9B

The carbon steel annealing experiment described in Example 1-9A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 0.50% natural gasto the feed gas with the amount of natural gas being 2.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with twotimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 850°C.

EXAMPLE 1-9C

The carbon steel annealing experiment described in Example 1-9A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 1.0% natural gas tothe feed gas with the amount of natural gas being 4.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with fourtimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 850°C. However, it would not result in an acceptable process for brightannealing steel at 850° C.

EXAMPLE 1-9D

The carbon steel annealing experiment described in Example 1-9A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 2.0% natural gas tothe feed gas with the amount of natural gas being 8.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with eighttimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 850°C. However, it would not result in an acceptable process for brightannealing steel at 850° C.

EXAMPLE 1-10A

The carbon steel annealing experiment described in Example 1-1 wasrepeated using the same furnace, samples, location of feed gas, natureof feed gas device, flow rate and composition of feed gas, and annealingprocedure with the exception of using 750° C. temperature. The amount ofnatural gas added in this example was equal to the stoichiometric amountrequired for converting residual oxygen present in the feed nitrogen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed withstoichiometric amount of natural gas into a continuous heat treatingfurnace through an open tube located in the transition zone would resultin an acceptable process for oxide annealing steel at 750° C. However,it would not result in an acceptable process for bright annealing steelat 750° C.

EXAMPLE 1-10B

The carbon steel annealing experiment described in Example 1-10A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 0.50% natural gasto the feed gas with the amount of natural gas being 2.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with twotimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 750°C.

EXAMPLE 1-10C

The carbon steel annealing experiment described in Example 1-10A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 1.0% natural gas tothe feed gas with the amount of natural gas being 4.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with fourtimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 750°C. However, it would not result in an acceptable process for brightannealing steel at 750° C.

EXAMPLE 1-10D

The carbon steel annealing experiment described in Example 1-10A wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 2.0% natural gas tothe feed gas with the amount of natural gas being 8.0 timesstoichiometric amount required for converting residual oxygen present inthe feed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with eighttimes the stoichiometric amount of natural gas into a continuous heattreating furnace through an open tube located in the transition zonewould result in an acceptable process for oxide annealing steel at 750°C. However, it would not result in an acceptable process for brightannealing steel at 750° C.

EXAMPLE 1-11

Carbon steel was treated by the process of Example 1-1 with theexception of feeding the gaseous mixture through a 1/2 in. diametersteel tube fitted with a 3/4 in. diameter elbow with the opening facingdown, i.e., facing the samples and the open feed tube inserted into thefurnace through the cooling zone to introduce feed gas into the heatingzone of the furnace 60 at location 74 in FIG. 4. The feed gas enteringthe heating zone of the furnace impinged directly on the samplessimulating the introduction of feed gas through an open tube into theheating zone of the furnace. The amount of natural gas used was 0.25% ofthe feed gas. It was therefore equal to the stoichiometric amountrequired for the complete conversion of residual oxygen present in thefeed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe oxidized non-uniformly. The residual oxygen present in the feednitrogen was converted in the heating zone to a mixture of carbonmonoxide, carbon dioxide, and moisture. The presence of large amount ofresidual oxygen and the ratios of pCO/pCO₂ and pH₂ /pH₂ O equal to orless than 1.0 in the cooling zone were ideal for oxidizing the surfaceof the samples in a controlled manner (see Table 1). However, thesamples were oxidized non-uniformly. A detailed analysis of the fluidflow and temperature profiles in the furnace indicated that the feed gaswas introduced at high velocity and was not heated to a temperature highenough to cause oxygen and natural gas to react completely in thevicinity of the open feed tube, resulting in the direct impingement ofthe cold nitrogen with unreacted oxygen on the samples and concomitantlyin non-uniform oxidation.

Thus a conventional open feed tube cannot be used to introducenon-cryogenically produced nitrogen pre-mixed with stoichiometric amountof natural gas into the heating zone of a continuous furnace to produceuniform and controlled oxidized steel samples.

EXAMPLES 1-12 TO 1-14

The carbon steel annealing experiment described in Example 1-11 wasrepeated three times using the same furnace, temperature, samples,location of feed gas, nature of feed gas device, flow rate andcomposition of feed gas, and annealing procedure with the exception ofadding 0.5, 1.0, and 3.0% natural gas to the feed gas with the amount ofnatural gas being 2.0, 4.0, and 12.0 times stoichiometric amount,respectively, required for converting residual oxygen present in thefeed nitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with these procedures were found tobe oxidized non-uniformly. Thus a conventional open feed tube cannot beused to introduce non-cryogenically produced nitrogen pre-mixed with2.0, 4.0, and 12.0 times the stoichiometric amount of natural gas intothe heating zone of a continuous furnace to produce uniform andcontrolled oxidized steel samples.

EXAMPLE 1-15

The carbon steel annealing experiment described in Example 1-11 wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 5.0% natural gas tothe feed gas with the amount of natural gas being 20.0 timesstoichiometric amount, respectively, required for converting residualoxygen present in the feed nitrogen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a surface finish that was partly bright and partly oxidized. Thus aconventional open feed tube cannot be used to introducenon-cryogenically produced nitrogen pre-mixed with 20 times thestoichiometric amount of natural gas into the heating zone of acontinuous furnace to produce uniform and controlled oxidized or brightsteel samples.

EXAMPLE 1-16

The carbon steel annealing experiment described in Example 1-11 wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of introduce feed gas intothe heating zone of the furnace 60 at location 76 in FIG. 4. The amountof natural gas used was equal to the stoichiometric amount required forconverting residual oxygen present in the feed nitrogen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe oxidized non-uniformly. Thus a conventional open feed tube once againcannot be used to introduce non-cryogenically produced nitrogenpre-mixed with the stoichiometric amount of natural gas into the heatingzone of a continuous furnace to produce uniform and controlled oxidizedsteel samples.

EXAMPLE 1-17

The carbon steel annealing experiment described in Example 1-16 wasrepeated using the same furnace, temperature, samples, location of feedgas, nature of feed gas device, flow rate and composition of feed gas,and annealing procedure with the exception of adding 3.0% natural gas inthe gaseous feed mixture. The amount of natural gas used was 12.0 timesthe stoichiometric amount required for converting residual oxygenpresent in the feed nitrogen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tobe oxidized non-uniformly. Thus a conventional open feed tube once againcannot be used to introduce non-cryogenically produced nitrogenpre-mixed with 12.0 times the stoichiometric amount of natural gas intothe heating zone of a continuous furnace to produce uniform andcontrolled oxidized steel samples.

EXAMPLE 1-18

The carbon steel annealing experiment described in Example 1-11 wasrepeated using the same furnace, samples, location of feed gas, natureof feed gas device, flow rate and composition of feed gas, and annealingprocedure with the exception of using 950° C. temperature, as shown inTable 1. The amount of natural gas added was equal to the stoichiometricamount required for converting residual oxygen present in the feednitrogen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe oxidized non-uniformly. Thus a conventional open feed tube cannot beused to introduce non-cryogenically produced nitrogen pre-mixed with thestoichiometric amount of natural gas into the heating zone of acontinuous furnace to produce uniform and controlled oxidized or brightsteel samples.

EXAMPLES 1-19 TO 1-20

The carbon steel annealing experiment described in Example 1-18 wasrepeated two times using the same furnace, temperature, samples,location of feed gas, nature of feed gas device, flow rate andcomposition of feed gas, and annealing procedure with the exception ofadding 0.5 and 1.0 natural gas to the feed gas with the amount ofnatural gas being 2.0 and 4.0 times stoichiometric amount, respectively,required for converting residual oxygen present in the feed nitrogen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with these procedures were found tobe oxidized non-uniformly. Thus a conventional open feed tube cannot beused to introduce non-cryogenically produced nitrogen pre-mixed with 2.0and 4.0 times the stoichiometric amount of natural gas into the heatingzone of a continuous furnace to produce uniform and controlled oxidizedsteel samples.

Analysis of the data of Table 1 relating to the above examples showedthat a straight open tube located in the heating zone of the furnacecannot be used to introduce non-cryogenically produced nitrogenpre-mixed with natural gas into the furnace and produce controlledoxidized and/or bright, oxide-free annealed carbon steel samples.Although oxygen present in the feed gas was converted to a mixture ofcarbon monoxide, carbon dioxide and moisture in the heating and coolingzones of the furnace, it was not converted completely to the abovementioned gases in the vicinity of the feed area. This is because of thefact that the feed gas enters the furnace at high velocity and thereforedoes not get time to heat up and cause residual oxygen and natural gaspresent in it to react. This results in the impingement of the feed gaswith unreacted oxygen on the samples and consequently their uncontrolledoxidation.

The data in Table 1 showed that a straight open tube located in thetransition zone of the furnace can be used under certain conditions tooxide-anneal carbon steel in a controlled manner using a mixture ofnon-cryogenically produced nitrogen and natural gas. It cannot howeverbe used for bright, oxide-free annealing steel. The acceptable operatingregion for controlled and uniform oxide annealing steel is shown in FIG.7.

Since most of the heat treaters generally switch back and forth betweencontrolled oxide annealing and bright (oxide-free) annealing, processesfor oxide annealing and bright, oxide-free annealing carbon steelutilizing the same furnace without making major process changes havebeen developed by introducing a gaseous feed mixture in the heating zoneof the furnace as will be shown by the results of samples processed andreported in Table 2 below.

                                      TABLE 2                                     __________________________________________________________________________                       Example 2-1                                                                          Example 2-2                                                                           Example 2-3                                                                          Example 2-4                                                                          Example                                                                               Example               __________________________________________________________________________                                                            2-5B                  Heat Treatment Temperature, °C.                                                           1,100  1,100   1,100  1,100  1,100   1,100                 Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350     350                   Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                               Heating Zone                             (Location 72)                                                                        (Location 74)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                             (Location 76)         Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                              Modified                                 Porous Porous  Porous Porous Porous  Porous                                   Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                              Diffuser                                 (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)             Feed Gas Composition                                                          Nitrogen, %        99.50  99.50   99.50  99.40  99.25   99.25                 Oxygen, %          0.50   0.50    0.50   0.60   0.75    0.75                  Natural Gas* (Methane), %                                                                        2.00   2.00    2.00   2.00   2.00    2.50                  Heating Zone Atmosphere Composition                                           Oxygen, ppm        <2     <3      <4     <4     <4      <3                    Carbon Monoxide, % 1.00   1.10    0.95   1.10   1.40    1.50                  Carbon Dioxide, %  0.00   0.00    0.00   0.00   0.00    0.00                  Hydrogen, %        2.80   3.00    2.50   2.55   2.50    3.50                  Methane, %         0.60   0.40    0.55   0.50   0.60    0.75                  Dew Point, °C.                                                                            - 58.6 -58.8   -58.3  -58.3  -58.1   -58.2                 Cooling Zone Atmosphere Composition                                           Oxygen, ppm        550    <5      <7     <8     ˜10                                                                             <6                    Carbon Monoxide, % 0.50   0.90    0.85   0.95   1.25    1.30                  Carbon Dioxide, %  0.04   0.00    0.00   0.00   0.01    0.01                  Hydrogen, %        1.00   2.60    2.50   2.55   2.50    3.10                  Methane, %         1.42   0.71    0.75   0.80   0.77    0.98                  Dew Point, °C.                                                                            -9.0   -27.9   -31.8  -25.7  -20.9   -21.9                 Quality of Heat Treated Samples                                                                  Uniform,                                                                             Uniform Uniform                                                                              Uniform                                                                              Uniform Uniform                                  Tightly                                                                              Bright  Bright Bright Bright  Bright                                   Packed Oxide                 with Slight                                                                   Straw                                                                         Color                         __________________________________________________________________________                       Example 2-6                                                                          Example 2-7A                                                                          Example 2-7B                                                                         Example 2-7C                                                                          Example                                                                              Example               __________________________________________________________________________                                                            2-9                   Heat Treatment Temperature, °C.                                                           1,100  1,100   1,100  1,100   1,050  1,050                 Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350     350    350                   Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                          Heating                                                                              Heating Zone                             (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                         (Location                                                                            (Location 76)         Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                 Porous Porous  Porous Porous  Porous Porous                                   Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                 (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)             Feed Gas Composition                                                          Nitrogen, %        99.20  99.50   99.50  99.50   99.75  99.70                 Oxygen, %          0.80   0.50    0.50   0.50    0.25   0.30                  Natural Gas* (Methane), %                                                                        2.50   0.50    1.00   1.50    2.00   2.00                  Heating Zone Atmosphere Composition                                           Oxygen, ppm        <2     <6      <4     <3      <9     <6                    Carbon Monoxide, % 1.55   0.40    0.85   1.00    0.50   0.60                  Carbon Dioxide, %  0.00   0.10    0.05   0.01    0.00   0.00                  Hydrogen, %        3.50   0.50    1.45   2.40    2.30   2.30                  Methane, %         1.10   0.04    0.05   0.08    0.65   0.70                  Dew Point, °C.                                                                            -58.2  -8.8    -11.3  -22.3   -58.3  -58.5                 Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <7     <9      <7     <4      <8     <8                    Carbon Monoxide, % 1.35   0.15    0.60   1.40    0.50   0.60                  Carbon Dioxide, %  0.02   0.35    0.32   0.01    0.00   0.00                  Hydrogen, %        3.05   0.15    0.90   2.20    2.30   2.25                  Methane, %         0.96   0.06    0.07   0.22    0.57   0.65                  Dew Point, °C.                                                                            -19.6  +6.4    +11.1  -3.6    -52.6  -44.4                 Quality of Heat Treated Samples                                                                  Uniform                                                                              Uniform,                                                                              Uniform,                                                                             Uniform Uniform                                                                              Uniform                                  Bright Tightly Tightly                                                                              Bright  Bright Bright                                          Packed  Packed                                                                Oxide   Oxide                                       __________________________________________________________________________                       Example 2-10                                                                         Example 2-11                                                                          Example 2-12                                                                         Example 2-13                                                                         Example                                                                              Example                __________________________________________________________________________                                                           2-15                   Heat Treatment Temperature, °C.                                                           1,050  1,050   1,050  1,050  1,050  1,050                  Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350    350                    Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                             Modified                                  Porous Porous  Porous Porous Porous Porous                                    Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                             Diffuser                                  (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.65  99.60   99.60  99.55  99.50  99.50                  Oxygen, %          0.35   0.40    0.40   0.45   0.50   0.50                   Natural Gas* (Methane), %                                                                        2.00   2.00    2.00   2.25   2.25   2.00                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <6     <6      <4     <4     <4     <5                     Carbon Monoxide, % 0.60   0.75    0.80   0.90   0.95   0.90                   Carbon Dioxide, %  0.00   0.00    0.00   0.00   0.00   0.00                   Hydrogen, %        2.10   2.10    2.60   2.65   2.70   2.40                   Methane, %         0.80   0.80    0.70   0.80   0.90   0.80                   Dew Point, °C.                                                                            -58.3  -58.3   -58.3  -58.3  -58.3  -58.4                  Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <9     <9      <5     <5     <7     <6                     Carbon Monoxide, % 0.60   0.70    0.75   0.85   0.90   0.85                   Carbon Dioxide, %  0.00   0.00    0.00   0.00   0.00   0.00                   Hydrogen, %        2.20   2.10    2.60   2.70   2.70   2.40                   Methane, %         0.69   0.73    0.78   0.86   0.90   0.78                   Dew Point, °C.                                                                            -41.3  -35.9   -41.2  -36.9  -33.1  -32.6                  Quality of Heat Treated Samples                                                                  Uniform                                                                              Uniform Uniform                                                                              Uniform                                                                              Uniform                                                                              Uniform                                   Bright Bright  Bright Bright Bright Bright                 __________________________________________________________________________                       Example 2-16                                                                          Example 2-17A                                                                          Example 2-17B                                                                          Example 2-17C                                                                           Example                __________________________________________________________________________                                                           2-18                   Heat Treatment Temperature, °C.                                                           1,050   1,000    1,000    1,000     1,000                  Flow Rate of Feed Gas, SCFH                                                                      350     350      350      350       350                    Feed Gas Location  Heating Zone                                                                          Heating Zone                                                                           Heating Zone                                                                           Heating Zone                                                                            Heating Zone                              (Location 76)                                                                         (Location 76)                                                                          (Location 76)                                                                          (Location 76)                                                                           (Location 76)          Type of Feed Device                                                                              Modified                                                                              Modified Modified Modified  Modified                                  Porous  Porous   Porous   Porous    Porous                                    Diffuser                                                                              Diffuser Diffuser Diffuser  Diffuser                                  (FIG. 3C)                                                                             (FIG. 3C)                                                                              (FIG. 3C)                                                                              (FIG. 3C) (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.50   99.70    99.70    99.70     99.75                  Oxygen, %          0.50    0.30     0.30     0.30      0.25                   Natural Gas* (Methane), %                                                                        1.50    2.00     1.50     1.00      2.00                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <5      <3       <6       ˜10 <4                     Carbon Monoxide, % 1.00    0.40     0.60     0.35      0.35                   Carbon Dioxide, %  0.00    0.00     0.00     0.01      0.00                   Hydrogen, %        2.15    1.20     1.20     1.05      1.10                   Methane, %         0.40    1.10     0.40     0.40      1.10                   Dew Point, °C.                                                                            -29.4   -57.7    -33.8    -29.1     -57.9                  Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <6      <9       <9       ˜11 <7                     Carbon Monoxide, % 1.00    0.40     0.60     0.35      0.35                   Carbon Dioxide, %  0.01    0.00     0.00     0.01      0.00                   Hydrogen, %        2.20    1.60     1.20     1.00      1.70                   Methane, %         0.35    1.02     0.37     0.33      1.02                   Dew Point, °C.                                                                            -22.1   -57.7    -29.1    -23.6     -57.9                  Quality of Heat Treated Samples                                                                  Uniform Uniform  Uniform  Uniform   Uniform                                   Bright  Bright   Bright   Bright    Bright                                                              with Slight                                                                   Straw Color                      __________________________________________________________________________                        Example 2-19                                                                          Example 2-20                                                                           Example 2-21                                                                          Example 2-22                                                                           Example                 __________________________________________________________________________                                                          2-23                    Heat Treatment Temperature, °C.                                                            1,000   1,000    950     950      950                     Flow Rate of Feed Gas, SCFH                                                                       350     350      350     350      350                     Feed Gas Location   Heating Zone                                                                          Heating Zone                                                                           Heating Zone                                                                          Heating Zone                                                                           Heating Zone                                (Location 76)                                                                         (Location 76)                                                                          (Location 76)                                                                         (Location 76)                                                                          (Location 76)           Type of Feed Device Modified                                                                              Modified Modified                                                                              Modified Modified                                    Porous  Porous   Porous  Porous   Porous                                      Diffuser                                                                              Diffuser Diffuser                                                                              Diffuser Diffuser                                    (FIG. 3C)                                                                             (FIG. 3C)                                                                              (FIG. 3C)                                                                             (FIG. 3C)                                                                              (FIG. 3C)               Feed Gas Composition                                                          Nitrogen, %         99.80   99.85    99.90   99.925   99.95                   Oxygen, %           0.20    0.15     0.10    0.075    0.05                    Natural Gas* (Methane), %                                                                         2.00    2.00     2.00    1.75     1.25                    Heating Zone Atmosphere Composition                                           Oxygen, ppm         <3      <3       <3      <2       <3                      Carbon Monoxide, %  0.30    0.20     0.10    0.10     0.10                    Carbon Dioxide, %   0.00    0.00     0.00    0.00     0.00                    Hydrogen, %         1.05    0.9      0.80    0.50     0.30                    Methane, %          1.10    1.12     1.32    1.12     0.60                    Dew Point, °C.                                                                             -57.9   -57.9    -58.1   -57.7    -33.8                   Cooling Zone Atmosphere Composition                                           Oxygen, ppm         <6      <8       ˜10                                                                             <87      <7                      Carbon Monoxide, %  0.25    0.25     0.15    0.10     0.10                    Carbon Dioxide, %   0.00    0.00     0.00    0.00     0.00                    Hydrogen, %         1.70    1.60     1.30    0.50     0.30                    Methane, %          1.02    0.87     1.18    1.10     0.60                    Dew Point, °C.                                                                             -58.0   -57.9    -58.1   -57.9    -58.1                   Quality of Heat Treated Samples                                                                   Uniform Uniform  Uniform Uniform  Uniform                                     Bright  Bright   Bright  Bright   Bright                  __________________________________________________________________________     *Natural gas was mixed with nitrogen and added as a percent of total          noncryogenically produced nitrogen.                                      

EXAMPLE 2-1

The carbon steel annealing experiment described in Example 1-14 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, and annealing procedure with the exceptions ofadding 2.0% natural gas in the gaseous feed mixture and introducing thegaseous feed mixture into the heating zone of the furnace (Location 72in FIG. 4) through a modified porous diffuser. A generally cylindricalshaped diffuser 40 shown in FIG. 3C comprising a top half 44 of 3/4 in.diameter, 6 in. long porous Inconel material was assembled. The porousInconel material had about forty-seven 0.094 inch diameter holes persquare inch. The holes were staggered with about 0.156 inch distancebetween the two closest holes. The number of holes and hole patternprovided about 33% open area for the flow of gaseous mixture. Bottomhalf 46 of diffuser 40 was a gas impervious Inconel with one end 42 ofdiffuser 40 capped and the other end 43 attached to a 1/2 in. diameterstainless steel feed tube inserted into the furnace 60 through thecooling end vestibule 68. The bottom half 46 of diffuser 40 waspositioned parallel to the parts 16' (prime) being treated thusessentially directing the flow of feed gas towards the hot ceiling ofthe furnace and preventing the direct impingement of the feed gas withunreacted oxygen on the samples 16'. The amount of natural gas used inthis example was 8.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surfaces. The residualoxygen present in the feed nitrogen was converted in the heating zone toa mixture of carbon monoxide and moisture. The presence of high pCO/pCO₂(>2.8) and pH₂ /pH₂ O (>1.3) ratios probably reduced the surface of thesamples in the heating zone. The surface of the samples was howeveroxidized in the cooling zone due to the presence of large amount ofresidual oxygen (see Table 2).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 8.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 72) would result in an acceptableprocess for oxide annealing steel at 1,100° C. Since the modified porousdiffuser was located only 12 in. (Location 72) away from the coolingzone, all the residual oxygen present in the feed gas was not reactedwith natural gas prior to entering the cooling zone. The residual oxygen(550 ppm) present in the cooling zone caused the samples to oxidize in acontrolled manner, as shown in Table 2. Therefore, the introduction ofgaseous feed mixture into the heating zone (Location 72) through amodified porous diffuser would always result in uniformly oxidizedsamples provided that the amount of natural gas or any other hydrocarbonused is more than the stoichiometric amount required for the completeconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

EXAMPLE 2-2

The carbon steel annealing experiment described in Example 2-1 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of introducing the gaseous feed mixtureinto the heating zone of the furnace (Location 74 in FIG. 4). The amountof natural gas used In this example was 8.0 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 5 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture. The presence of substantial amounts of carbon monoxide andhydrogen or the presence of high pCO/pCO₂ (>2.8) and pH₂ /pH₂ O (>1.3)ratios both in the heating and cooling zones resulted in reducing thesurface of the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 8.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 74) would result in an acceptableprocess for bright, oxide-free annealing steel at 1,100° C.

This example therefore showed are critical steps of the process involvesthe method of introducing the mixture into the furnace. For example,most of the residual oxygen present in the feed gas was converted tocarbon monoxide and moisture simply by placing the modified porousdiffuser 30 in. (Location 74) away from the cooling zone instead of only12 in. (Location 72). Therefore, the introduction of gaseous feedmixture into the heating zone (Location 74) through a modified porousdiffuser at 1,100° C. would always result in bright, oxide-free sampleswith non-cryogenically produced nitrogen provided that the amount ofnatural gas or any other hydrocarbon used is more than thestoichiometric amount required for the complete conversion of residualoxygen to a mixture of carbon dioxide and moisture, that the amount ishigh enough to yield pCO/pCO₂ greater than 2.8 and pH₂ /pH₂ O greaterthan 1.3 both in the heating and cooling zones, and that the residualoxygen level in both the heating and cooling zones is less than 10 ppm.

EXAMPLE 2-3

The carbon steel annealing experiment described in Example 2-1 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of introducing the gaseous feed mixtureinto the heating zone of the furnace (Location 76 in FIG. 4). The amountof natural gas used in this example was 8.0 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. This example once againshowed the critical nature of placing the modified diffuser in thefurnace. For example, most of the residual oxygen present in the feedgas was once again converted to carbon monoxide and moisture simply bymoving the modified porous diffuser from 12 in. (Location 72) to 40 in.(Location 76) away from the cooling zone. Therefore, the introduction ofnon-cryogenically produced nitrogen into the heating zone (Location 76)through a modified porous diffuser at 1,100° C. would always result inuniform bright, oxide-free samples provided that the amount of naturalgas or any other hydrocarbon used is more than the stoichiometric amountrequired for the complete conversion of residual oxygen to a mixture ofcarbon dioxide and moisture, that the amount is high enough to yieldpCO/pCO₂ greater than 2.8 and pH₂ /pH₂ O greater than 1.3 both in theheating and cooling zones, and that the residual oxygen level in boththe heating and cooling zones is less than 10 ppm.

The incoming steel material and the steel sample heat treated in thisexample were examined for extent of decarburization or carburization.Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in thenon-cryogenically produced nitrogen atmosphere pre-mixed with naturalgas produced decarburization of approximately 0.006 inches. Thedecarburization of steel sample was probably caused by the presence ofhigh dew point in the cooling zone.

EXAMPLE 2-4

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, and annealing procedurewith the exception of using non-cryogenically produced nitrogencontaining 99.4% N₂ and 0.6% O₂. The amount of natural gas used in thisexample was approximately 6.7 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 8 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture, as shown in Table 2.

This example once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,100° C. can beused to bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.8 and pH₂ /pH₂ O greater than 1.3 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-5A

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, and annealing procedurewith the exception of using non-cryogenically produced nitrogencontaining 99.25 N₂ and 0.75 O₂. The amount of natural gas used in thisexample was approximately 5.3 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright surface. The surface of the samples however had aslight straw color, making the surface finish to be marginallyacceptable. The residual oxygen present in the feed nitrogen wasconverted almost completely (approximately 10 ppm) in the heating andcooling zones to a mixture of carbon monoxide and moisture.

This example once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,100° C. can beused to bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.8 and pH₂ /pH₂ O greater than 1.3 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm. This example also showed that theminimum amount of natural gas required for bright annealing steel isabout 5.0 times the stoichiometric amount needed for complete conversionof residual oxygen present in the feed nitrogen to a mixture of carbondioxide and moisture.

EXAMPLE 2-5B

The carbon steel annealing experiment described in Example 2-5A wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 2.5% natural gas insteadof 2.0%. The amount of natural gas used in this example wasapproximately 6.7 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The surface of each samplewas also free of straw color. The residual oxygen present in the feednitrogen was converted almost completely (less than 6 ppm) in theheating and cooling zones to a mixture of carbon monoxide and moisture.

This example once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,100° C. can beused to bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.8 and pH₂ /pH₂ O greater than 1.3 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in this exampleproduced decarburization of approximately 0.007 inches. The extent ofdecarburization in the sample heat treated in this example was higherthan the one treated in Example 2-3, probably due to the presence ofhigher dew point in the cooling zone (see Table 2).

EXAMPLE 2-6

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, and annealing procedurewith the exception of using non-cryogenically produced nitrogencontaining 99.2% N₂ and 0.8% O₂. The amount of natural gas used in thisexample was approximately 6.3 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 7 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture.

This example once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,100° C. can beused to bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.8 and pH₂ /pH₂ O greater than 1.3 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-7A

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.50% natural gasinstead of 2.0%. The amount of natural gas used in this example wasapproximately 2.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide surface finishes. The residual oxygenpresent in the feed nitrogen was converted almost completely (less than8 ppm) in the heating and cooling zones to a mixture of carbon monoxide,carbon dioxide, and moisture, as shown in Table 2. The samples wereoxidized due to the presence of low pCO/pCO₂ (<2.8) and pH₂ /pH₂ O(<1.3) ratios in the cooling zone.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,100° C. can be used tocontrolled oxide anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ lowerthan 2.8 and pH₂ /pH₂ O lower than 1.3 in the cooling zone.

EXAMPLE 2-7B

The carbon steel annealing experiment described in Example 2-7A wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 1.0% natural gas. Theamount of natural gas used in this example was approximately 4.0 timesthe stoichiometric amount required for the conversion of residual oxygento a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide surface finishes. The residual oxygenpresent in the feed nitrogen was converted almost completely (less than8 ppm) in the heating and cooling zones to a mixture of carbon monoxide,carbon dioxide, and moisture, as shown in Table 2. The samples wereoxidized due to the presence of low pCO/pCO₂ (<2.8) and pH₂ /pH₂ O(<1.3) ratios in the cooling zone.

This example once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,100° C. can beused to oxide anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ lowerthan 2.8 and pH₂ /pH₂ O lower than 1.3 in the cooling zones.

EXAMPLE 2-7C

The carbon steel annealing experiment described in Example 2-7A wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 1.5% natural gas. Theamount of natural gas used in this example was approximately 6.0 timesthe stoichiometric amount required for the conversion of residual oxygento a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 4 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 2.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,100° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.8 and pH₂ /pH₂ O greater than 1.3 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-8

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, samples, flow rate of feed gas, typeand location of gas feeding device, and annealing procedure with theexceptions of using 1,050° C. temperature and non-cryogenically producednitrogen containing 99.75% N₂ and 0.25% O₂. The amount of natural gasused in this example was 16.0 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 9 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,050° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.6 and pH₂ /pH₂ O greater than 1.4 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in thenon-cryogenically produced nitrogen atmosphere pre-mixed with naturalgas in this example produced marginal decarburization--the depth ofdecarburization was approximately 0.001 inches. This example thereforeshowed that the extent of decarburization in the samples heat treated inthe non-cryogenically produced nitrogen atmosphere pre-mixed withnatural gas can be controlled by controlling dew point both in thecooling as well as heating zones of a continuous furnace.

EXAMPLES 2-9 TO 2-15

The carbon steel annealing experiment described in Example 2-8 wasrepeated seven times in Examples 2-9 to 2-15 using the same furnace,samples, flow rate of feed gas, temperature, type and location of gasfeeding device, and annealing procedure with the exceptions of using theamount of natural gas varying from 2.0 to 2.25% and non-cryogenicallyproduced nitrogen containing 99.70 to 99.50% N₂ and 0.30 to 0.50% O₂, asshown in Table 2. The amount of natural gas used in these examplesvaried from 8.0 to approximately 13.3 times the stoichiometric amountrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture.

Steel samples heat treated in these examples were found to haveuniformly bright, oxide-free surfaces. The residual oxygen present inthe feed nitrogen was converted almost completely (less than 9 ppm) inthe heating and cooling zones to a mixture of carbon monoxide andmoisture.

These examples once again showed that a modified porous diffuser locatedwell inside the heating zone of the furnace operated at 1,050° C. can beused to bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.6 and pH₂ /pH₂ O greater than 1.4 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

Examination of incoming material showed neither carburization ordecarburization. The steel sample heat treated in Example 2-10 in thenon-cryogenically produced nitrogen atmosphere pre-mixed with naturalgas in this example also produced neither decarburization norcarburization. This example therefore showed that non-cryogenicallyproduced nitrogen atmosphere pre-mixed with natural gas can be used forneutral hardening carbon steel by carefully controlling the dew pointboth in the cooling and heating zones of a continuous furnace.

EXAMPLE 2-16

The carbon steel annealing experiment described in Example 2-15 wasrepeated using the same furnace, samples, temperature, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exceptions of using 1.5% natural gas. Theamount of natural gas used in this example was approximately 6.0 timesthe stoichiometric amount required for the conversion of residual oxygento a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,050° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than 6.0 times the stoichiometric amountrequired for the complete conversion of residual oxygen to a mixture ofcarbon dioxide and moisture, that the amount is high enough to yieldpCO/pCO₂ greater than 2.6 and pH₂ /pH₂ O greater than 1.4 both in theheating and cooling zones, and that the residual oxygen level in boththe heating and cooling zones is less than 10 ppm.

EXAMPLE 2-17A

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, samples, flow rate of feed gas, typeand location of gas feeding device, and annealing procedure with theexceptions of using 1,000° C. temperature and non-cryogenically producednitrogen containing 99.70% N₂ and 0.30% O₂. The amount of natural gasused in this example was approximately 13.3 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 9 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,000° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-17B

The carbon steel annealing experiment described in Example 2-17A wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 1.5% natural gas. Theamount of natural gas used in this example was 10.0 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 9 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,000° C. can be used tobright, and oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that tile amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-17C

The carbon steel annealing experiment described in Example 2-17A wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 1.0% natural gas. Theamount of natural gas used in this example was 6.7 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright surfaces. The surface of the samples however had aslight straw color, making the surface finish marginally acceptable. Theresidual oxygen present in the feed nitrogen was converted almostcompletely (less than 11 ppm) in the heating and cooling zones to amixture of carbon monoxide, carbon dioxide, and moisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,000° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLES 2-18 AND 2-19

The carbon steel annealing experiment described in Example 2-17 wasrepeated two times in Examples 2-18 to 2-19 using the same furnace,samples, flow rate of feed gas, temperature, type and location of gasfeeding device, and annealing procedure with the exception of usingnon-cryogenically produced nitrogen containing 99.75 and 99.80% N₂ and0.25 to 0.20% O₂, as shown in Table 2. The amount of natural gas used inthese examples was 16.0 and 20.0 times the stoichiometric amount,respectively, required for the conversion of residual oxygen to amixture of carbon dioxide and moisture.

Steel samples heat treated in these examples were found to haveuniformly bright, oxide-free surfaces. The residual oxygen present inthe feed nitrogen was converted almost completely (less than 7 ppm) inthe heating and cooling zones to a mixture of carbon monoxide andmoisture.

These examples showed that a modified porous diffuser located wellinside the heating zone of the furnace operated at 1,000° C. can be usedto bright, oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-20

The carbon steel annealing experiment described in Example 2-17 wasrepeated using the same furnace, samples, flow rate of feed gas,temperature, type and location of gas feeding device, and annealingprocedure with the exception of using non-cryogenically producednitrogen containing 99.85% N₂ and 0.15% O₂, as shown in Table 2. Theamount of natural gas used in this example was approximately 26.7 timesthe stoichiometric amount required for the conversion of residual oxygento a mixture of carbon dioxide and moisture.

Steel samples heat treated in these examples were found to haveuniformly bright, oxide-free surfaces. The residual oxygen present inthe feed nitrogen was converted almost completely (less than 8 ppm) inthe heating and cooling zones to a mixture of carbon monoxide andmoisture. However both the belt and the inside of the furnace were foundto begin sooting slightly, indicating that the process conditions usedin this example are not ideal for long term heat treatment. Morespecifically, the test results revealed that it would be desirable toreduce the amount of natural gas used in the gaseous feed mixture toprevent sooting in the furnace.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 1,000° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.50 and pH₂ /pH₂ O greater than 1.5 both in the heating andcooling zones, that the amount is not too high to begin sooting insidethe furnace, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 2-21

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, samples, flow rate of feed gas, typeand location of gas feeding device, and annealing procedure with theexceptions of using 950° C. temperature, and non-cryogenically producednitrogen containing 99.90% N₂ and 0.10% O₂, as shown in Table 2. Theamount of natural gas used tn this example was 40.0 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (approximately 10ppm) in the heating and cooling zones to a mixture of carbon monoxideand moisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 950° C. can be used tobright, and oxide-free anneal carbon steel with non-cryogenicallyproduced nitrogen provided that the amount of natural gas used is about40 times the stoichiometric amount required for the complete conversionof residual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.4 and pH₂ /pH₂ Ogreater than 1.6 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

Examination of incoming material showed neither carburization ordecarburization. The steel sample heat treated in the non-cryogenicallyproduced nitrogen atmosphere pre-mixed with natural gas in this examplealso produced neither decarburization nor carburization. This exampletherefore showed that non-cryogenically produced nitrogen atmospherepre-mixed with natural gas can be used for neutral hardening carbonsteel by carefully controlling the dew point both in the cooling andheating zones of a continuous furnace.

EXAMPLE 2-22

The carbon steel annealing experiment described in Example 2-21 wasrepeated using the same furnace, samples, temperature, flow rate of feedgas, type and location of gas feeding device, and annealing procedurewith the exceptions of using non-cryogenically produced nitrogencontaining 99.925% N₂ and 0.075% O₂ and adding 1.75% natural gas, asshown in Table 2. The amount of natural gas used in this example wasapproximately 46.7 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted completely in the heating and coolingzones to a mixture of carbon monoxide and moisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 950° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than 40 times the stoichiometric amountrequired for the complete conversion of residual oxygen to a mixture ofcarbon dioxide and moisture, that the amount is high enough to yieldpCO/pCO₂ greater than 2.4 and pH₂ /pH₂ O greater than 1.6 both in theheating and cooling zones, and that the residual oxygen level in boththe heating and cooling zones is less than 10 ppm.

Examination of incoming material showed neither carburization ordecarburization. The steel sample heat treated in the non-cryogenicallyproduced nitrogen atmosphere pre-mixed with natural gas in this examplealso produced neither decarburization nor carburization. This exampletherefore showed that non-cryogenically produced nitrogen atmospherepre-mixed with natural gas can be used for neutral hardening carbonsteel by carefully controlling the dew point both in the cooling andheating zones of a continuous furnace.

EXAMPLE 2-23

The carbon steel annealing experiment described in Example 2-21 wasrepeated using the same furnace, samples, temperature, flow rate of feedgas, type and location of gas feeding device, and annealing procedurewith the exceptions of using non-cryogenically produced nitrogencontaining 99.95% N₂ and 0.05% O₂ and adding 1.25% natural gas. Theamount of natural gas used In this example was 50 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted completely in the heating and coolingzones to a mixture of carbon monoxide and moisture.

This example showed that a modified porous diffuser located well insidethe heating zone of the furnace operated at 950° C. can be used tobright, oxide-free anneal carbon steel with non-cryogenically producednitrogen provided that the amount of natural gas or any otherhydrocarbon used is more than 40 times the stoichiometric amountrequired for the complete conversion of residual oxygen to a mixture ofcarbon dioxide and moisture, that the amount is high enough to yieldpCO/pCO₂ greater than 2.4 and pH₂ /pH₂ O greater than 1.6 both in theheating and cooling zones, and that the residual oxygen level in boththe heating and cooling zones is less than 10 ppm.

Examination of incoming material showed neither carburization ordecarburization. The steel sample heat treated in the non-cryogenicallyproduced nitrogen atmosphere pre-mixed with natural gas in this examplealso produced neither decarburization nor carburization. This exampletherefore showed that non-cryogenically produced nitrogen atmospherepre-mixed with natural gas can be used for neutral hardening carbonsteel by carefully controlling the dew point both in the cooling andheating zones of a continuous furnace.

A number of additional experiments were conducted at 950° C. temperatureto define the operating window for controlled oxide and bright,oxide-free annealing of steel. The results of these experiments are setout in Table 3 and discussed in detail below.

                                      TABLE 3                                     __________________________________________________________________________                       Example 3-1                                                                              Example 3-2                                                                              Example 3-3A                                                                             Example                   __________________________________________________________________________                                                        3-4                       Heat Treatment Temperature, °C.                                                           950        950        950        950                       Flow Rate of Feed Gas, SCFH                                                                      350        350        350        350                       Feed Gas Location  Heating Zone                                                                             Heating Zone                                                                             Heating Zone                                                                             Heating Zone                                 (Location 76)                                                                            (Location 76)                                                                            (Location 76)                                                                            (Location 76)             Type of Feed Device                                                                              Modified Porous                                                                          Modified Porous                                                                          Modified Porous                                                                          Modified Porous                              Diffuser (FIG. 3C)                                                                       Diffuser (FIG. 3C)                                                                       Diffuser (FIG.                                                                           Diffuser (FIG. 3C)        Feed Gas Composition                                                          Nitrogen, %        99.50      99.50      99.50      99.75                     Oxygen, %          0.50       0.50       0.50       0.25                      Natural Gas* (Methane), %                                                                        0.25       1.00       3.00       0.25                      Heating Zone Atmosphere Composition                                           Oxygen, ppm        <8         <6         <10        <8                        Carbon Monoxide, % 0.0        0.45       0.95       0.10                      Carbon Dioxide, %  0.17       0.17       0.00       0.05                      Hydrogen, %        0.00       1.40       3.00       0.20                      Methane, %         0.03       0.23       1.68       0.11                      Dew Point, °C.                                                                            1.3        7.7        -22.9      -24.9                     Cooling Zone Atmosphere Composition                                           Oxygen, ppm        330        190        140        300                       Carbon Monoxide, % 0.00       0.45       0.75       0.10                      Carbon Dioxide, %  0.20       0.03       0.02       0.06                      Hydrogen, %        0.00       1.20       3.10       0.10                      Methane, %         0.03       0.40       2.44       0.12                      Dew Point, °C.                                                                            7.7        - 2.8      -14.7      --                        Quality of Heat Treated Samples                                                                  Uniform, Tightly                                                                         Uniform, Tightly                                                                         Mixture of Bright                                                                        Uniform, Tightly                             Packed Oxide                                                                             Packed Oxide                                                                             Oxide      Packed                    __________________________________________________________________________                                                        Oxide                                        Example 3-5                                                                              Example 3-6                                                                              Example 3-7                                                                              Example                   __________________________________________________________________________                                                        3-8                       Heat Treatment Temperature, °C.                                                           950        950        950        950                       Flow Rate of Feed Gas, SCFH                                                                      350        350        350        350                       Feed Gas Location  Heating Zone                                                                             Heating Zone                                                                             Heating Zone                                                                             Heating Zone                                 (Location 76)                                                                            (Location 76)                                                                            (Location 76)                                                                            (Location 76)             Type of Feed Device                                                                              Modified Porous                                                                          Modified Porous                                                                          Modified Porous                                                                          Modified Porous                              Diffuser (FIG. 3C)                                                                       Diffuser (FIG. 3C)                                                                       Diffuser (FIG.                                                                           Diffuser (FIG. 3C)        Feed Gas Composition                                                          Nitrogen, %        99.75      99.75      99.90      99.90                     Oxygen, %          0.25       0.25       0.10       0.10                      Natural Gas* (Methane), %                                                                        1.00       3.00       0.25       0.50                      Heating Zone Atmosphere Composition                                           Oxygen, ppm        <7         <7         <6         <3                        Carbon Monoxide, % 0.50       --         0.00       0.20                      Carbon Dioxide, %  0.00       0.00       0.09       0.03                      Hydrogen, %        1.50       3.00       0.10       0.65                      Methane, %         0.28       1.56       0.16       0.15                      Dew Point, °C.                                                                            -30.4      -32.8      -12.6      -18.9                     Cooling Zone Atmosphere Composition                                           Oxygen, ppm        140        110        230        110                       Carbon Monoxide, % 0.25       0.45       0.00       0.20                      Carbon Dioxide, %  0.01       0.01       0.04       0.01                      Hydrogen, %        1.10       3.40       0.10       0.55                      Methane, %         0.52       2.40       0.13       0.22                      Dew Point, °C.                                                                            -15.2      -28.7      -12.2      -23.0                     Quality of Heat Treated Samples                                                                  Mixture of Bright &                                                                      Mixture of Bright &                                                                      Uniform, Tightly                                                                         Mixture of Bright                            Oxide      Oxide      Packed Oxide                                                                             & Oxide                   __________________________________________________________________________     *Natural gas was mixed with nitrogen and added as a percent of total          noncryogenically produced nitrogen.                                      

EXAMPLE 3-1

The carbon steel annealing experiment described in Example 2-21 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, and annealing procedure with the exceptions of usingnon-cryogenically produced nitrogen containing 99.5% N₂ and 0.5% O₂,adding 0.25% natural gas in the gaseous feed mixture, and introducingthe gaseous feed mixture into the heating zone of the furnace (Location76 in FIG. 4) through a modified porous diffuser. A generallycylindrical shaped diffuser 40 shown in FIG. 3C comprising a top half 44of 3/4 in. diameter, 6 in. long sintered Inconel material with averagepore size of 20 microns and open porosity varying from 40-50% suppliedby the Mott Metallurgical Corporation was assembled. Bottom half 46 ofdiffuser 40 was a gas impervious Inconel with one end 42 of diffuser 40capped and the other end 43 attached to a 1/2 in. diameter stainlesssteel feed tube inserted into the furnace 60 through the cooling endvestibule 68. The bottom half 46 of diffuser 40 was positioned parallelto the parts 16' (prime) being treated thus essentially directing theflow of feed gas towards the hot ceiling of the furnace and preventingthe direct impingement of the feed gas with unreacted oxygen on thesamples 16'. The amount of natural gas used in this example was equal tothe stoichiometric amount required for the conversion of residual oxygento a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating zone toa mixture of carbon dioxide and moisture, as shown in Table 2. Thepresence low pCO/pCO₂ (<2.4) and pH₂ /pH₂ O (<1.6) ratios helped inoxidizing the surface of the samples in the heating zone. The surface ofthe samples was oxidized further in the cooling zone due to the presenceof large amount of residual oxygen (see Table 3), resulting in uniformand controlled oxidation of the surface of the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith the stoichiometric amount of natural gas into a continuous heattreating furnace through a modified porous diffuser located in theheating zone (Location 76) would result in an acceptable process foroxide annealing steel at 950° C.

EXAMPLE 3-2

The carbon steel annealing experiment described in Example 3-1 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of adding 1.0% natural gas to the gaseousfeed mixture. The amount of natural gas used in this example was 4.0times the stoichiometric amount required for the conversion of residualoxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted almost completely(less than 6 ppm) in the heating zone to a mixture of carbon monoxide,carbon dioxide, and moisture, as shown in Table 3. The presence of lowpH₂ /pH₂ O (<1.6) ratio in the heating zone was ideal for oxidizing thesurface of the samples. The surface of the samples was oxidized furtherin the cooling zone due to the presence of large amount of residualoxygen (See Table 3), resulting in uniform and controlled oxidation ofthe surface of the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 4.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 76) would result in an acceptableprocess for oxide annealing steel at 950° C.

EXAMPLE 3-3A

The carbon steel annealing experiment described in Example 3-1 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of adding 3.0% natural gas to the gaseousfeed mixture. The amount of natural gas used in this example was 12.0times the stoichiometric amount required for the conversion of residualoxygen to a mixture of carbon dioxide and moisture.

The surface of steel samples heat treated in accord with this procedurewere found to be partially oxidized and partially bright. The residualoxygen present in the feed nitrogen was converted almost completely(less than 10 ppm) in the heating zone to a mixture of carbon monoxideand moisture, as shown in Table 3. The composition of the gas in theheating and cooling zones showed the presence of high pCO/pCO₂ (>2.4)and pH₂ /pH₂ O (>1.6) ratios both of which are ideal for reducing thesurface of the samples. The surface of the samples however was partiallyoxidized due to the presence of large amount of residual oxygen in thecooling zone (see Table 3).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 12.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 76) would result in anunacceptable process for oxide and/or bright annealing steel at 950° C.

EXAMPLE 3-3B

The carbon steel annealing experiment described in Example 3-1 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of adding 5.0% natural gas to the gaseousfeed mixture. The amount of natural gas used in this example was 20.0times the stoichiometric amount required for the conversion of residualoxygen to a mixture of carbon dioxide and moisture.

The surface of steel samples heat treated in accord with this procedurewere found to be partially oxidized and partially bright. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with 20.0times the stoichiometric amount of natural gas into a continuous heattreating furnace through a modified porous diffuser located in theheating zone (Location 76) would result in an unacceptable process foroxide and/or bright annealing steel at 950° C.

EXAMPLE 3-4

The carbon steel annealing experiment described in Example 3-1 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, amount of natural gas, type of gas feeding device, and annealingprocedure with the exception of using non-cryogenically producednitrogen containing 99.75% N₂ and 0.25% O₂. The amount of natural gasused in this example was 2.0 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted almost completely(less than 8 ppm) in the heating zone to a mixture of carbon monoxide,carbon dioxide, and moisture, as shown in Table 3. The presence of highpH₂ /pH₂ O (>1.6) ratio in the heating zone was ideal for reducing thesurface of the samples. However, the surface of the samples was oxidizedin the cooling zone due to the presence of low pCO/pCO₂ ratio and largeamount of residual oxygen (see Table 3), resulting in uniform andcontrolled oxidation of the surface of the samples.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 2.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 76) would result in an acceptableprocess for oxide annealing steel at 950° C.

EXAMPLE 3-5

The carbon steel annealing experiment described in Example 3-4 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of using 1.0% natural gas. The amount ofnatural gas used in this example was 8.0 times the stoichiometric amountrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture.

The surface of steel samples heat treated in accord with this procedurewere found to be partially oxidized and partially bright. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with 8.0times the stoichiometric amount of natural gas into a continuous heattreating furnace through a modified porous diffuser located in theheating zone (Location 76) would result in an unacceptable process foroxide and/or bright annealing steel at 950° C.

EXAMPLE 3-6

The carbon steel annealing experiment described in Example 3-4 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of using 3.0% natural gas. The amount ofnatural gas used in this example was 24.0 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe partially oxidized and partially bright. Thus the introduction ofnon-cryogenically produced nitrogen pre-mixed with 24.0 times thestoichiometric amount of natural gas into a continuous heat treatingfurnace through a modified porous diffuser located in the heating zone(Location 76) would result in an unacceptable process for oxide and/orbright annealing steel at 950° C.

EXAMPLE 3-7

The carbon steel annealing experiment described in Example 3-4 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, amount of natural gas, type of gas feeding device, and annealingprocedure with the exception of using non-cryogenically producednitrogen containing 99.9% N₂ and 0.1% O₂. The amount of natural gas usedin this example was 5.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted almost completely(less than 6 ppm) in the heating zone to a mixture of carbon dioxide andmoisture. The presence of low pCO/pCO₂ (<2.4) and pH₂ /pH₂ O (<1.6)ratios in the heating and cooling zones and the presence of large amountof residual oxygen in the cooling zone were ideal for oxidizing thesurface of the samples (see Table 3).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 5.0 times the stoichiometric amount of natural gas into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone (Location 76) would result in an acceptableprocess for oxide annealing steel at 950° C.

EXAMPLE 3-8

The carbon steel annealing experiment described in Example 3-7 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type of gas feeding device, and annealingprocedure with the exception of using 0.50% natural gas. The amount ofnatural gas used in this example was 10.0 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tobe partially oxidized and partially bright surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with 10.0times the stoichiometric amount of natural gas into a continuous heattreating furnace through a modified porous diffuser located in theheating zone (Location 76) would result in an unacceptable process foroxide and/or bright annealing steel at 950° C.

The Examples 2-1 to 2-7 showed that non-cryogenically produced nitrogencould be used to bright anneal steel at 1,100° C. temperature providedthat more than about 5.0 times the stoichiometric amount of natural gasrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture was used and that a modified diffuser was used tointroduce the gaseous feed mixture in the heating zone of the furnace.Likewise, the Examples 2-8 to 2-23 showed that non-cryogenicallyproduced nitrogen could be used to bright anneal steel at 1,050° C.,1,000° C., and 950° C. temperatures provided that about 6.0, 13.0, and40.0 times, respectively, the stoichiometric amount of natural gasrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture was used. The above examples showed that theabsolute amount of natural gas required for bright annealing steelincreased with the increase in the level of residual oxygen in the feednitrogen. Additionally, the absolute amount of natural gas required forbright annealing steel decreased with an increase in the heat treatmenttemperature.

The results of Examples 3-1 to 3-8 showed that a non-cryogenicallyproduced nitrogen can be used to oxide anneal steel at 950° C. providedthat the amount of natural gas added to the feed nitrogen is between 1.0to about 7.0 times the stoichiometric amount required for the conversionof residual oxygen present in the feed nitrogen to a mixture of carbondioxide and moisture. The results also showed that the addition of 8.0to 24.0 times the stoichiometric amount of natural gas results inundesirable partially oxidized and partially bright surface.

The examples 2-1 to 2-23 and 3-1 to 3-8 relate to annealing using amodified porous diffuser or modified gas feed device to show that carbonsteel can be annealed at temperatures ranging from 950° C. to 1,100° C.with non-cryogenically produced nitrogen provided more thanstoichiometric amount of natural gas is added to the feed gas. Theprocess of the present invention employing a method of introducing thefeed gas into the furnace (e.g. using a modified porous diffuser)enables a user to perform oxide annealing and bright, oxide-freeannealing of carbon steel, as shown in FIG. 8. The operating regionsshown in FIG. 8 are considerably broader using the process of thepresent invention than those noted with conventional gas feed device, asis evident by comparing FIGS. 7 and 8. The above experiments thereforedemonstrate the importance of preventing the impingement of feed gaswith unreacted oxygen on the parts.

A number of carbon steel heat treating experiments were carried outusing a mixture of non-cryogenically produced nitrogen and propane. Theresults of these experiments are set out in Table 4 and discussed indetail below.

                                      TABLE 4                                     __________________________________________________________________________                       Example 4-1                                                                          Example 4-2                                                                           Example 4-3                                                                          Example 4-4                                                                          Example                                                                              Example                __________________________________________________________________________                                                           4-6                    Heat Treatment Temperature, °C.                                                           1,100  1,100   1,100  1,100  1,100  1,100                  Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350    350                    Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                             Modified                                  Porous Porous  Porous Porous Porous Porous                                    Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                             Diffuser                                  (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.50  99.30   99.00  99.00  99.00  99.00                  Oxygen, %          0.50   0.70    1.00   1.00   1.00   1.00                   Propane, %         0.20   0.20    0.20   0.25   0.28   0.40                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <5     <10     <4     <5     <4     <3                     Carbon Monoxide, % 0.55   0.45    0.20   0.45   0.65   0.95                   Carbon Dioxide, %  0.00   0.08    0.34   0.24   0.18   0.11                   Hydrogen, %        1.00   0.70    0.40   0.06   0.95   1.50                   Propane, %         0.02   0.01    0.00   0.00   0.01   0.05                   Dew Point, °C.                                                                            -58.3  - 10.0  5.0    5.0    0.5    -4.3                   Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <6     <8      <4     <5     <5     <4                     Carbon Monoxide, % 0.50   0.40    0.15   0.40   0.60   0.90                   Carbon Dioxide, %  0.00   0.09    0.35   0.25   0.18   0.12                   Hydrogen, %        0.90   0.65    0.30   0.60   0.90   1.40                   Propane, %         0.02   0.01    0.00   0.00   0.01   0.05                   Dew Point, °C.                                                                            -58.3  -10.0   5.0    5.0    0.50   -4.3                   Quality of Heat Treated Samples                                                                  Uniform                                                                              Uniform Uniform,                                                                             Uniform,                                                                             Uniform,                                                                             Uniform                                   Bright Bright  Tightly                                                                              Tightly                                                                              Tightly                                                                              Bright                                                   Packed Oxide                                                                         Packed Oxide                                                                         Packed Oxide                  __________________________________________________________________________                       Example 4-7                                                                          Example 4-8                                                                           Example 4-9                                                                          Example 4-10                                                                         Example                                                                              Example                __________________________________________________________________________                                                           4-12                   Heat Treatment Temperature, °C.                                                           1,050  1,050   1,050  1,050  1,050  1,050                  Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350    350                    Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                             Modified                                  Porous Porous  Porous Porous Porous Porous                                    Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                             Diffuser                                  (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.50  99.25   99.25  99.00  99.00  99.00                  Oxygen, %          0.50   0.75    0.75   1.00   1.00   1.00                   Propane, %         0.20   0.20    0.25   0.25   0.28   0.40                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <5     <4      <4     <4     <4     <5                     Carbon Monoxide, % 0.30   0.20    0.40   0.25   0.45   0.80                   Carbon Dioxide, %  0.05   0.18    0.12   0.29   0.22   0.14                   Hydrogen, %        0.75   0.40    0.80   0.50   0.80   1.40                   Propane, %         0.05   0.00    0.01   0.00   0.01   0.04                   Dew Point, °C.                                                                            -13.0  -2.2    -4.1   6.0    6.1    -4.2                   Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <7     <4      <5     <4     <5     <5                     Carbon Monoxide, % 0.30   0.20    0.40   0.25   0.45   0.80                   Carbon Dioxide, %  0.05   0.19    0.12   0.29   0.22   0.14                   Hydrogen, %        0.70   0.40    0.75   0.45   0.80   1.40                   Propane, %         0.05   0.00    0.01   0.00   0.01   0.04                   Dew Point, °C.                                                                            -13.0  -2.2    -4.1   6.0    6.0    -4.1                   Quality of Heat Treated Samples                                                                  Uniform                                                                              Uniform,                                                                              Uniform                                                                              Uniform,                                                                             Uniform,                                                                             Uniform                                   Bright Tightly Bright Tightly                                                                              Tightly                                                                              Bright                                           Packed Oxide   Packed Oxide                                                                         Packed Oxide                  __________________________________________________________________________                       Example 4-13                                                                         Example 4-14                                                                          Example 4-15                                                                         Example 4-16                                                                         Example                                                                              Example                __________________________________________________________________________                                                           4-18                   Heat Treatment Temperature, °C.                                                           1,000  1,000   1,000  1,000  1,000  1,000                  Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350    350                    Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                             Modified                                  Porous Porous  Porous Porous Porous Porous                                    Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                             Diffuser                                  (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.50  99.50   99.25  99.25  99.25  99.25                  Oxygen, %          0.50   0.50    0.75   0.75   0.75   0.75                   Propane, %         0.20   0.25    0.20   0.25   0.28   0.32                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <6     <4      <5     <5     <5     <4                     Carbon Monoxide, % 0.30   0.50    0.20   0.40   0.60   0.75                   Carbon Dioxide, %  0.09   0.01    0.20   0.14   0.09   0.06                   Hydrogen, %        0.70   1.10    0.45   0.80   1.10   1.45                   Propane, %         0.01   0.04    0.00   0.01   0.04   0.05                   Dew Point, °C.                                                                            -9.3   -35.0   0.10   -1.5   -6.1   -15.6                  Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <8     <7      <5     <6     <7     <7                     Carbon Monoxide, % 0.30   0.45    0.20   0.40   0.60   0.75                   Carbon Dioxide, %  0.07   0.01    0.20   0.14   0.09   0.06                   Hydrogen, %        0.70   1.05    0.40   0.80   1.10   1.40                   Propane, %         0.01   0.04    0.01   0.01   0.03   0.06                   Dew Point, °C.                                                                            -9.2   -35.2   0.00   -1.5   -6.2   -15.0                  Quality of Heat Treated Samples                                                                  Uniform                                                                              Uniform Uniform,                                                                             Mixture of                                                                           Uniform                                                                              Uniform                                   Bright Bright  Tightly                                                                              Bright &                                                                             Bright Bright                                                   Packed Oxide                                                                         Oxide                                __________________________________________________________________________                       Example 4-19                                                                         Example 4-20                                                                          Example 4-21                                                                         Example 4-22                                                                         Example                                                                              Example                __________________________________________________________________________                                                           4-24                   Heat Treatment Temperature, °C.                                                           1,000  1,000   1,000  950    950    950                    Flow Rate of Feed Gas, SCFH                                                                      350    350     350    350    350    350                    Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                          Heating Zone                                                                         Heating Zone                                                                         Heating                                                                              Heating Zone                              (Location 76)                                                                        (Location 76)                                                                         (Location 76)                                                                        (Location 76)                                                                        (Location                                                                            (Location 76)          Type of Feed Device                                                                              Modified                                                                             Modified                                                                              Modified                                                                             Modified                                                                             Modified                                                                             Modified                                  Porous Porous  Porous Porous Porous Porous                                    Diffuser                                                                             Diffuser                                                                              Diffuser                                                                             Diffuser                                                                             Diffuser                                                                             Diffuser                                  (FIG. 3C)                                                                            (FIG. 3C)                                                                             (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)              Feed Gas Composition                                                          Nitrogen, %        99.00  99.00   99.00  99.50  99.50  99.50                  Oxygen, %          1.00   1.00    1.00   0.50   0.50   0.50                   Propane, %         0.28   0.40    0.55   0.20   0.25   0.32                   Heating Zone Atmosphere Composition                                           Oxygen, ppm        <4     <5      <4     <7     <8     <6                     Carbon Monoxide, % 0.50   0.85    1.20   0.30   0.50   0.85                   Carbon Dioxide, %  0.24   0.15    0.07   0.09   0.03   0.00                   Hydrogen, %        0.80   1.40    2.00   0.65   1.00   1.70                   Propane, %         0.01   0.06    0.07   0.02   0.05   0.06                   Dew Point, °C.                                                                            5.0    1.0     -9.5   -6.0   -26.0  -58.3                  Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <5     <5      <8     11     12     ˜10              Carbon Monoxide, % 0.50   0.80    1.15   0.30   0.50   0.80                   Carbon Dioxide, %  0.24   0.15    0.08   0.07   0.02   0.00                   Hydrogen, %        0.80   1.40    1.95   0.65   1.00   1.60                   Propane, %         0.01   0.05    0.10   0.02   0.05   0.07                   Dew Point, °C.                                                                            5.1    1.5     -9.6   -6.5   -26.2  -58.3                  Quality of Heat Treated Samples                                                                  Uniform,                                                                             Uniform Uniform                                                                              Uniform,                                                                             Mixture                                                                              Uniform                                   Tightly                                                                              Bright  Bright Tightly                                                                              Oxide &                                                                              Bright                                    Packed Oxide          Packed Oxide                                                                         Bright                        __________________________________________________________________________                         Example 4-25                                                                          Example 4-26                                                                          Example 4-27                                                                           Example 4-28                                                                          Example                 __________________________________________________________________________                                                          4-29                    Heat Treatment Temperature, °C.                                                            950      950     950      900     900                     Flow Rate of Feed Gas, SCFH                                                                       350      350     350      350     350                     Feed Gas Location   Heating Zone                                                                           Heating Zone                                                                          Heating Zone                                                                           Heating Zone                                                                          Heating Zone                                (Location 76)                                                                          (Location 76)                                                                         (Location 76)                                                                          (Location                                                                             (Location 76)           Type of Feed Device Modified Modified                                                                              Modified Modified                                                                              Modified                                    Porous   Porous  Porous   Porous  Porous                                      Diffuser Diffuser                                                                              Diffuser Diffuser                                                                              Diffuser                                    (FIG. 3C)                                                                              (FIG. 3C)                                                                             (FIG. 3C)                                                                              (FIG. 3C)                                                                             (FIG. 3C)               Feed Gas Composition                                                          Nitrogen, %         99.25    99.25   99.25    99.50   99.50                   Oxygen, %           0.75     0.75    0.75     0.50    0.50                    Propane, %          0.32     0.55    0.63     0.20    0.28                    Heating Zone Atmosphere Composition                                           Oxygen, ppm         <8       <6      <6       <10     11                      Carbon Monoxide, %  0.75     1.25    1.25     0.25    0.70                    Carbon Dioxide, %   0.07     0.00    0.00     0.10    0.00                    Hydrogen, %         1.35     2.20    2.30     0.60    1.30                    Propane, %          0.10     0.13    0.20     0.02    0.06                    Dew Point, °C.                                                                             -15.3    -58.3   -58.3    -9.6    -35.0                   Cooling Zone Atmosphere Composition                                           Oxygen, ppm         15       12      13       18      18                      Carbon Monoxide, %  0.75     1.20    1.20     0.25    0.65                    Carbon Dioxide, %   0.07     0.00    0.00     0.10    0.00                    Hydrogen, %         1.35     2.10    2.20     0.60    1.25                    Propane, %          0.08     0.12    0.15     0.03    0.08                    Dew Point, °C.                                                                             -15.6    -58.0   -58.9    -10.0   -34.5                   Quality of Heat Treated Samples                                                                   Mixture of                                                                             Uniform Uniform  Non-Uniform                                                                           Mixture of                                  Bright & Bright  Bright   Oxide   Bright &                                    Oxide    With Slight                                                                           With Slight      Oxide                                                Straw   Straw                                                                 Color   Color                                    __________________________________________________________________________     *Propane was mixed with nitrogen and added as a percent of total              noncryogenically produced nitrogen.                                      

EXAMPLE 4-1

The carbon steel annealing experiment described in Example 2-3 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.2% propane instead of2.0% natural gas. The amount of propane used in this example was 2.0times the stoichiometric amount required for the conversion of residualoxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 6 ppm)in the heating and cooling zones to a mixture of carbon monoxide andmoisture, as shown in Table 4. The presence of high pCO/pCO₂ (>2.8) andpH₂ /pH₂ O (>1.3) ratios in both the heating and cooling zones resultedin reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,100° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.8 and pH₂ /pH₂ Ogreater than 1.3 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in thenon-cryogenically produced nitrogen atmosphere pre-mixed with propane inthis example produced marginal decarburization--the depth ofdecarburization was approximately 0.0038 inches.

EXAMPLE 4-2

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.3% N₂ and 0.7% O₂. The amount of propaneused in this example was approximately 1.5 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 10 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.8) and pH₂ /pH₂ O (>1.3) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,100° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.8 and pH₂ /pH₂ Ogreater than 1.3 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-3

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.0% N₂ and 1.0% O₂. The amount of propaneused in this example was equal to the stoichiometric amount required forthe conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating andcooling zones to a mixture of carbon dioxide, carbon monoxide, andmoisture. The presence of low pCO/pCO₂ (<2.8) and pH₂ /pH₂ O (<1.3)ratios both in the heating and cooling zones resulted in oxidizing thesamples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith the stoichiometric amount of propane into a continuous heattreating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,100° C.

EXAMPLE 4-4

The carbon steel annealing experiment described in Example 4-3 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.25% propane instead of0.2%, as shown in Table 4. The amount of propane used in this examplewas 1.25 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layers on the surface. The presenceof low pCO/pCO₂ (<2.8) and pH₂ /pH₂ O (<1.3) ratios both in the heatingand cooling zones resulted in oxidizing the samples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 1.25 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,100° C.

EXAMPLE 4-5

The carbon steel annealing experiment described in Example 4-3 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.28% propane instead of0.2%, as shown in Table 4. The amount of propane used in this examplewas 1.40 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure once again werefound to have uniform, tightly packed oxide layers on the surface. Thepresence of low pCO/pCO₂ (<2.8) and pH₂ /pH₂ O (<1.3) ratios both in theheating and cooling zones resulted in oxidizing the samples (see Table4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 1.40 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,100° C.

EXAMPLE 4-6

The carbon steel annealing experiment described in Example 4-3 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.40% propane instead of0.2%, as shown in Table 4. The amount of propane used in this examplewas 2.0 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 4 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.8) and pH₂ /pH₂ O (>1.3) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,100° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.8 and pH₂ /pH₂ Ogreater than 1.3 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in thenon-cryogenically produced nitrogen atmosphere pre-mixed with propane inthis example produced decarburization of approximately 0.0055 inches.

EXAMPLE 4-7

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, samples, flow rate and composition offeed gas, type and location of gas feeding-device, and annealingprocedure with the exception of using 1,050° C. temperature instead of1,100° C. The amount of propane used in this example was 2.0 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surfaces. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 7 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.6) and pH₂ /pH₂ O (>1.4) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,050° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.6 and pH₂ /pH₂ Ogreater than 1.4 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-8

The carbon steel annealing experiment described in Example 4-7 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.25% N₂ and 0.75% O₂. The amount ofpropane used in this example was 1.33 times the stoichiometric amountrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave uniform, tightly packed oxide layers on the surface. The residualoxygen present in the feed nitrogen was converted in the heating andcooling zones to a mixture of carbon dioxide, carbon monoxide, andmoisture. The presence of low pCO/pCO₂ (<2.6) and pH₂ /pH₂ O (<1.4)ratios both in the heating and cooling zones resulted in oxidizing thesamples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 1.33 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,050° C.

EXAMPLE 4-9

The carbon steel annealing experiment described in Example 4-8 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.25% propane instead of0.2%, as shown in Table 4. The amount of propane used in this examplewas approximately 1.7 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 5 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.6) and pH₂ /pH₂ O (>1.4) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,050° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.6 and pH₂ /pH₂ Ogreater than 1.4 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-10

The carbon steel annealing experiment described in Example 4-9 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.0% N₂ and 1.0% O₂, as shown in Table 4.The amount of propane used in this example was equal to 1.25 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating andcooling zones to a mixture of carbon dioxide, carbon monoxide, andmoisture. The presence of low pCO/pCO₂ (<2.6) and pH₂ /pH₂ O (<1.4)ratios both in the heating and cooling zones resulted in oxidizing thesamples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 1.25 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,050° C.

EXAMPLE 4-11

The carbon steel annealing experiment described in Example 4-10 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.28% propane instead of0.25%, as shown in Table 4. The amount of propane used in this examplewas equal to 1.40 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with 1.40times the stoichiometric amount of propane into a continuous heattreating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,050° C.

EXAMPLE 4-12

The carbon steel annealing experiment described in Example 4-10 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.40% propane instead of0.25%, as shown in Table 4. The amount of propane used in this examplewas equal to 2.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 5 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.6) and pH₂ /pH₂ O (>1.4) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,050° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.6 and pH₂ /pH₂ Ogreater than 1.4 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-13

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, samples, flow rate and composition offeed gas, type and location of gas feeding device, and annealingprocedure with the exception of using 1,000° C. temperature instead of1,100° C., as shown in Table 4. The amount of propane used in thisexample was 2.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 7 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.5) and pH₂ /pH₂ O (>1.5) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,000° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.5 and pH₂ /pH₂ Ogreater than 1.5 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-14

The carbon steel annealing experiment described in Example 4-13 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.25% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas 2.5 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. Thus the introduction ofnon-cryogenically produced nitrogen into the heating zone through amodified porous diffuser at 1,000° C. would result in uniform bright,oxide-free samples provided that the amount of propane or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 4-15

The carbon steel annealing experiment described in Example 4-13 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.25% N₂ and 0.75% O₂. The amount ofpropane used in this example was 1.33 times the stoichiometric amountrequired for the conversion of residual oxygen to a mixture of carbondioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating andcooling zones to a mixture of carbon dioxide, carbon monoxide, andmoisture. The presence of low pCO/pCO₂ (<2.5) and pH₂ /pH₂ O (<1.5)ratios both in the heating and cooling zones resulted in oxidizing thesamples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 1.33 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,000° C.

EXAMPLE 4-16

The carbon steel annealing experiment described in Example 4-15 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.25% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas equal to 1.67 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a surface finish that was partly bright and partly oxidized. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon dioxide, carbonmonoxide, and moisture. The presence of high pCO/pCO₂ (>2.5) ratio bothin the heating and cooling zones was possibly responsible for reducingthe sample. However, the presence of pH₂ /pH₂ O ratio close to 1.5 bothin the heating and cooling zones resulted in partially oxidizing thesamples <see Table 4).

Thus the introduction of non-cryogenically produced nitrogen-pre-mixedwith 1.67 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would not result in an acceptable process for oxide orbright annealing steel at 1,000° C.

EXAMPLE 4-17

The carbon steel annealing experiment described in Example 4-15 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.28% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas equal to 1.87 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. The residual oxygen presentin the feed nitrogen was converted almost completely (less than 7 ppm)in the heating and cooling zones to a mixture of carbon monoxide, carbondioxide, and moisture, as shown in Table 4. The presence of highpCO/pCO₂ (>2.5) and pH₂ /pH₂ O (>1.5) ratios in both the heating andcooling zones resulted in reducing the surface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at1,000° C. would result in uniform bright, oxide-free samples providedthat the amount of propane or any other hydrocarbon used is more thanthe stoichiometric amount required for the complete conversion ofresidual oxygen to a mixture of carbon dioxide and moisture, that theamount is high enough to yield pCO/pCO₂ greater than 2.5 and pH₂ /pH₂ Ogreater than 1.5 both in the heating and cooling zones, and that theresidual oxygen level in both the heating and cooling zones is less than10 ppm.

EXAMPLE 4-18

The carbon steel annealing experiment described in Example 4-15 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.32% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas equal to approximately 2.1 times the stoichiometric amount requiredfor the conversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave uniformly bright, oxide-free surface. Thus the introduction ofnon-cryogenically produced nitrogen into the heating zone through amodified porous diffuser at 1,000° C. would result in uniform bright,oxide-free samples provided that the amount of propane or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 4-19

The carbon steel annealing experiment described in Example 4-17 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.0% N₂ and 1.0% O₂, as shown in Table 4.The amount of propane used in this example was 1.4 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. Thus theintroduction of non-cryogenically produced nitrogen pre-mixed with 1.4times the stoichiometric amount of propane into a continuous heattreating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 1,000° C.

EXAMPLE 4-20

The carbon steel annealing experiment described in Example 4-19 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.40% propane instead of0.28%, as shown in Table 4. The amount of propane used in this examplewas 2.0 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. Thus the introduction ofnon-cryogenically produced nitrogen into the heating zone through amodified porous diffuser at 1,000° C. would result in uniform bright,oxide-free samples provided that the amount of propane or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 4-21

The carbon steel annealing experiment described in Example 4-20 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.55% propane instead of0.40%, as shown in Table 4. The amount of propane used in this examplewas 2.75 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a uniformly bright, oxide-free surface. Thus the introduction ofnon-cryogenically produced nitrogen into the heating zone through amodified porous diffuser at 1,000° C. would result in uniform bright,oxide-free samples provided that the amount of propane or any otherhydrocarbon used is more than the stoichiometric amount required for thecomplete conversion of residual oxygen to a mixture of carbon dioxideand moisture, that the amount is high enough to yield pCO/pCO₂ greaterthan 2.5 and pH₂ /pH₂ O greater than 1.5 both in the heating and coolingzones, and that the residual oxygen level in both the heating andcooling zones is less than 10 ppm.

EXAMPLE 4-22

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, samples, flow rate and composition offeed gas, type and location of gas feeding device, and annealingprocedure with the exception of using 950° C. temperature instead of1,100° C., as shown in Table 4. The amount of propane used in thisexample was 2.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a uniform, tightly packed oxide layer on the surface. The residualoxygen present in the feed nitrogen was converted in the heating andcooling zones to a mixture of carbon dioxide, carbon monoxide, andmoisture, as shown In Table 4. The presence of pH₂ /pH₂ O ratio close to1.6 both in the heating and cooling zones and approximately 11 ppmoxygen in the cooling zone resulted in oxidizing the samples (see Table4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 2.0 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would result in an acceptable process for controlled oxideannealing steel at 950° C.

EXAMPLE 4-23

The carbon steel annealing experiment described in Example 4-22 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.25% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas 2.5 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a mixture of bright and oxidized finish on the surface. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon dioxide, carbonmonoxide, and moisture, as shown in Table 4. The presence ofapproximately 12 ppm oxygen in the cooling zone resulted in partiallyoxidizing the samples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 2.5 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would not result in an acceptable process for oxide orbright annealing steel at 950° C.

EXAMPLE 4-24

The carbon steel annealing experiment described in Example 4-22 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.32% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas 3.2 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a bright, oxide-free surface finish. The residual oxygen present inthe feed nitrogen was converted in the heating and cooling zones to amixture of carbon monoxide and moisture, as shown in Table 4. Thepresence of high pCO/pCO₂ (>2.4) and pH₂ /pH₂ O (>1.6) ratios in boththe heating and cooling zones resulted in reducing the surface of thesamples.

This example showed that the introduction of non-cryogenically producednitrogen into the heating zone through a modified porous diffuser at950° C. would result in uniform bright, oxide-free samples provided thatthe amount of propane or any other hydrocarbon used is more than thestoichiometric amount required for the complete conversion of residualoxygen to a mixture of carbon dioxide and moisture, that the amount ishigh enough to yield pCO/pCO₂ greater than 2.4 and pH₂ /pH₂ O greaterthan 1.6 both in the heating and cooling zones, and that the residualoxygen level in both the heating and cooling zones is close to 10 ppm.

Examination of incoming material showed neither carburization ordecarburization while the steel sample heat treated in thenon-cryogenically produced nitrogen atmosphere pre-mixed with propane inthis example produced decarburization of approximately 0.0048 inches.

EXAMPLE 4-25

The carbon steel annealing experiment described in Example 4-24 wasrepeated using the same furnace, temperature, samples, flow rate of feedgas, type and location of gas feeding device, amount of propane, andannealing procedure with the exception of using a non-cryogenicallyproduced nitrogen containing 99.25% N₂ and 0.75% O₂. The amount ofpropane used in this example was approximately 2.1 times thestoichiometric amount required for the conversion of residual oxygen toa mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a mixture of bright and oxidized finish on the surface. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon dioxide, carbonmonoxide, and moisture, as shown in Table 4. The presence ofapproximately 15 ppm oxygen in the cooling zone resulted in partiallyoxidizing the samples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith approximately 2.1 times the stoichiometric amount of propane into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone would not result in an acceptable processfor oxide or bright annealing steel at 950° C.

EXAMPLE 4-26

The carbon steel annealing experiment described in Example 4-25 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.55% propane instead of0.32%, as shown in Table 4. The amount of propane used in this examplewas approximately 3.7 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a bright surface finish. The surface of the samples appeared tohave slight straw coloration, making them marginally acceptable. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon monoxide and moisture,as shown in Table 4. The presence of high pCO/pCO₂ (>2.4) and pH₂ /pH₂ O(>1.6) ratios in both the heating and cooling zones resulted in reducingthe surface of the samples. However, the presence of approximately 12ppm of oxygen in the cooling zone resulted in slight straw color on thesurface of the samples.

This example showed that the introduction of non-cryogenically producednitrogen containing 0.75% oxygen into the heating zone through amodified porous diffuser at 950° C. would result in marginallyacceptable bright samples.

EXAMPLE 4-27

The carbon steel annealing experiment described in Example 4-25 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.63% propane instead of0.32%, as shown in Table 4. The amount of propane used in this examplewas approximately 4.2 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a bright surface finish. The surface of the samples appeared tohave slight straw coloration, making them marginally acceptable. Thebelt and the furnace showed signs of sooting, indicating that it wouldnot be desirable to use such a high flow rate of propane.

This example showed that the introduction of non-cryogenically producednitrogen containing 0.75% oxygen along with 0.63% propane into theheating zone through a modified porous diffuser at 950° C. would notresult in acceptable process for bright annealing samples.

EXAMPLE 4-28

The carbon steel annealing experiment described in Example 4-1 wasrepeated using the same furnace, samples, flow rate and composition offeed gas, type and location of gas feeding device, and annealingprocedure with the exception of using 900° C. temperature instead of1,100° C., as shown in Table 4. The amount of propane used in thisexample was 2.0 times the stoichiometric amount required for theconversion of residual oxygen to a mixture of carbon dioxide andmoisture.

Steel samples heat treated in accord with this procedure were found tohave a mixture of bright and oxidized finish on the surface. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon dioxide, carbonmonoxide, and moisture, as shown in Table 4. The presence ofapproximately 18 ppm oxygen in the cooling zone resulted in partiallyoxidizing the samples (see Table 4).

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith approximately 2.0 times the stoichiometric amount of propane into acontinuous heat treating furnace through a modified porous diffuserlocated in the heating zone would not result in an acceptable processfor oxide or bright annealing steel at 900° C.

EXAMPLE 4-29

The carbon steel annealing experiment described in Example 4-28 wasrepeated using the same furnace, temperature, samples, flow rate andcomposition of feed gas, type and location of gas feeding device, andannealing procedure with the exception of using 0.28% propane instead of0.20%, as shown in Table 4. The amount of propane used in this examplewas 2.8 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

Steel samples heat treated in accord with this procedure were found tohave a mixture of bright and oxidized finish on the surface. Theresidual oxygen present in the feed nitrogen was converted in theheating and cooling zones to a mixture of carbon monoxide and moisture,as shown in Table 4. The presence of more than 10 ppm of oxygen in theheating and cooling zones resulted in partially oxidizing the samples(see Table 4). Additionally, some sooting was seen on the belt,indicating that it would not be desirable to use equal to or more than0.28% propane in the furnace at 900° C.

Thus the introduction of non-cryogenically produced nitrogen pre-mixedwith 2.8 times the stoichiometric amount of propane into a continuousheat treating furnace through a modified porous diffuser located in theheating zone would not result in an acceptable process for oxide orbright annealing steel at 950° C.

DISCUSSION

The Examples 4-1 to 4-6 showed that non-cryogenically produced nitrogencould be used to bright anneal steel at 1,100° C. temperature providedthat about 1.5 times the stoichiometric amount of propane required forthe conversion of residual oxygen to a mixture of carbon dioxide andmoisture was used and that a modified diffuser was used to introduce thegaseous feed mixture in the heating zone of the furnace. The amount ofpropane required for bright annealing steel was considerably lower thanthat of natural gas probably due to higher reactivity of propane thatnatural gas (the auto ignition temperature of propane is 468° C.compared to 556° C. for natural gas). Examples 4-7 to 4-24 showed thatnon-cryogenically produced nitrogen could be used to bright anneal steelat 1,050° C., 1,000° C., and 950° C. temperatures provided that about1.7, 1.9, and 3.2 times, respectively, the stoichiometric amount ofpropane required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture was used. The above examples showed that theabsolute amount of propane required for bright annealing steel increasedwith the increase in the level of residual oxygen in the feed nitrogen.Additionally, the absolute amount of propane required for brightannealing steel decreased with an increase in the heat treatmenttemperature.

The above Examples showed that a non-cryogenically produced nitrogen canbe used to oxide anneal steel at 1,100°, 1,050°, 1,000°, and 950° C.provided that the amount of propane added to the feed nitrogen is lessthan 1.5, 1.7, 1.9, and 3.2 times, respectively, the stoichiometricamount required for the conversion of residual oxygen present in thefeed nitrogen to a mixture of carbon dioxide and moisture. The operatingregions for oxide and bright, oxide-free annealing of low carbon steelsusing a mixture of non-cryogenically produced nitrogen and propane areshown in FIG. 9.

A number of experiments were carried out for brazing bronze to carbonsteel using a mixture of non-cryogenically produced nitrogen and naturalgas. The results of these experiments are discussed in detail below.

                                      TABLE 5                                     __________________________________________________________________________                       Example 5-1                                                                          Example 5-2                                                                          Example 5-3                                  __________________________________________________________________________    Heat Treatment Temperature, °C.                                                           1,000  1,000  1,000                                        Flow Rate of Feed Gas, SCFH                                                                      350    350    350                                          Feed Gas Location  Heating Zone                                                                         Heating Zone                                                                         Heating Zone                                                    (Location 76)                                                                        (Location 76)                                                                        (Location 76)                                Type of Feed Device                                                                              Modified                                                                             Modified                                                                             Modified                                                        Porous Porous Porous                                                          Diffuser                                                                             Diffuser                                                                             Diffuser                                                        (FIG. 3C)                                                                            (FIG. 3C)                                                                            (FIG. 3C)                                    Feed Gas Composition                                                          Nitrogen, %        99.70  99.70  99.60                                        Oxygen, %          0.30   0.30   0.40                                         Natural Gas* (Methane), %                                                                        2.00   2.00   2.50                                         Heating Zone Atmosphere Composition                                           Oxygen, ppm        <3     <3     <3                                           Carbon Monoxide, % 0.50   0.50   0.70                                         Carbon Dioxide, %  0.00   0.00   0.01                                         Hydrogen, %        2.00   2.00   2.50                                         Methane, %         0.70   0.73   0.80                                         Dew Point, °C.                                                                            -57.7  -57.5  -57.3                                        Cooling Zone Atmosphere Composition                                           Oxygen, ppm        <9     <9     ˜10                                    Carbon Monoxide, % 0.45   0.50   0.55                                         Carbon Dioxide, %  0.00   0.00   0.01                                         Hydrogen, %        2.00   2.00   2.50                                         Methane, %         0.70   0.75   0.94                                         Dew Point, °C.                                                                            -38.4  -37.9  -36.7                                        Quality of Brazed Samples                                                                        Good   Good   Good                                         __________________________________________________________________________     *Natural gas was mixed with nitrogen and added as a percent of total          noncryogenically produced nitrogen.                                      

EXAMPLE 5-1

The heat treating procedure described in Example 2-17A was followedusing the same furnace, flow rate and composition of feed gas,temperature, and type and location of gas feeding device for brazingbronze to carbon steel using copper pre-forms. The non-cryogenicallyproduced nitrogen used in this example contained 99.70% nitrogen and0.30% residual oxygen, as shown in Table 5. The amount of natural gasadded was 2.0%. it was approximately 13.3 times the stoichiometricamount required for the conversion of residual oxygen to a mixture ofcarbon dioxide and moisture.

The carbon steel and bronze parts were brazed successfully with goodbraze flow in this example. The PSA N₂ -natural gas atmosphere providedoptimum braze spreading and fillet formation. Additionally, no voidformation was observed at the braze joint. Finally, the brazed carbonsteel and bronze part had a bright, oxide-free surface finish.

This example showed that non-cryogenically produced nitrogen atmospherepre-mixed with a hydrocarbon gas can be used for brazing bronze tocarbon steel.

EXAMPLE 5-2

The brazing experiment described in Example 5-2 was repeated using thesame furnace, flow rate and composition of feed gas, temperature, andtype and location of gas feeding device, as shown in Table 5.

The carbon steel and bronze parts were brazed successfully with goodbraze flow in this example. The PSA N₂ -natural gas atmosphere providedoptimum braze spreading and fillet formation. Additionally, no voidformation was observed at the braze joint. Finally, the brazed carbonsteel and bronze part had a bright, oxide-free surface finish.

This example once again showed that non-cryogenically produced nitrogenatmosphere pre-mixed with a hydrocarbon gas can be used for brazingbronze to carbon steel.

EXAMPLE 5-3

The brazing experiment described in Example 5-2 was repeated using thesame furnace, flow rate of feed gas, temperature, and type and locationof gas feeding device with the exceptions of using non-cryogenicallyproduced nitrogen containing 99.60% nitrogen and 0.40% oxygen and adding2.5% natural gas, as shown in Table 5. The amount of natural gas addedwas 12.5 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of carbon dioxide and moisture.

The carbon steel and bronze parts were brazed successfully with goodbraze flow in this example. The PSA N₂ -natural gas atmosphere providedoptimum braze spreading and fillet formation. Additionally, no voidformation was observed at the braze joint. Finally, the brazed carbonsteel and bronze part had a bright, oxide-free surface finish.

This example showed that non-cryogenically produced nitrogen atmospherepre-mixed with a hydrocarbon gas can be used for brazing bronze tocarbon steel.

Having thus described our invention what is desired to be secured byLetters Patent of the United States is set forth in the appended claims.

We claim:
 1. A method of generating an in-situ atmosphere inside furnaceused for performing brazing of metals, sealing of glass to metals,sintering metal and ceramic powders, or non-ferrous metal and alloyannealing processes wherein said process comprises the steps of:heatingsaid furnace to a temperature above 700° C.; injecting into a hot zoneof the said furnace gaseous nitrogen generated by a non-cryogenic meanscontaining up to 5% by volume oxygen together with a hydrocarbon gas,said hydrocarbon gas injected into said furnace with a flow rate varyingfrom above about 1.5 times the stoichiometric amount required for acomplete conversion of oxygen to a mixture of moisture and carbondioxide, in a manner to permit said reaction of oxygen and saidhydrocarbon gas to be essentially complete prior to said mixturecontacting parts being subjected to a given process; and exposing saidparts to said temperature and said atmosphere for a time sufficient tocomplete said process.
 2. A method according to claim 1 wherein saidresidual oxygen is converted to a mixture of moisture and carbonmonoxide.
 3. A method according to claim 1 wherein said residual oxygenis converted to carbon dioxide, moisture, carbon monoxide or mixturesthereof.
 4. A method according to claim 1 wherein nitrogen generated bynon-cryogenic means contained up to about 1.0% by volume oxygen.
 5. Amethod according to claim 1 wherein said furnace is a continuous furnacewith integrated heating and cooling zones.
 6. A method according toclaim 1 wherein said furnace is a continuous furnace with a heating zoneand a quench cooling zone.
 7. A method according to claim 1 wherein saidhydrocarbon gas is selected from alkanes such as methane, ethane,propane, and butane; alkenes such as ethylene, propylene, and butene;alcohols such as methanol, ethanol, and propanol; ethers such asdimethyl ether, diethyl ether, and methyl ethyl ether; and commercialfeedstocks such as natural gas, petroleum gas, cooking gas, coke ovengas, town gas, exothermic gas, and endothermic gas.
 8. A methodaccording to claim 1 wherein said furnace is heated to a temperature ofbetween 700° C. and 1,250° C.
 9. A method according to claim 7 whereinsaid hydrocarbon is natural gas or methane injected in an amount greaterthan 5.0 times to above about 40.0 times the stoichiometric amountrequired for the conversion of residual oxygen to a mixture of moistureand carbon dioxide.
 10. A method according to claim 7 wherein saidhydrocarbon is propane injected in an amount greater than 1.5 times toabove 3.2 times the stoichiometric amount required for the conversion ofresidual oxygen to a mixture of moisture and carbon dioxide.